Another 10 blasts hit Baghdad early on Thursday while U.S. paratroopers secured an airfield in northern Iraq, possibly in preparation for a second front to the Iraq war.

About 1,000 U.S. paratroopers from the U.S. 173rd Airborne Brigade parachuted into the north of the country and seized an airfield in Kurdish-controlled territory under the cover of darkness.

"Approximately 1,000 troops went in," said Lt.-Col. Thomas Collins, spokesman for the army's Southern European Task Force. "I can only tell you yes, they've gone in. They're on the ground," he said.

Collins did not say exactly where in the north the troops had gone in. The unit of the 173rd Airborne is based in Vicenza, Italy.

"The important thing about that is it permits the American infantry division in Germany with a significant number of tanks and 17,000 troops to fly in here over the next couple of weeks," said Retired Maj.-Gen. Lewis MacKenzie.

Meanwhile, the Iraqi capital city was rattled by about 10 explosions at 3:45 a.m. Thursday. Some of the blasts were heard near the city, according to a Reuters correspondent. As well, anti-aircraft fire could be heard overhead.

Other military developments:

• An explosion at a marketplace in a residential area of Baghdad kills 15 and wounds 30. The U.S. is accused of firing on the market. The Pentagon says it never fired on the area.
• Warplanes pounded forward Iraqi position in the north of the country in an attempt to open a second front. Local Kurds cheered after each of the five large explosions targeting Iraqi government lines.
• The U.S. is sending its high-tech 4th Infantry Division and other units to the Persian Gulf for a total deployment of 30,000 additional troops.
• Between 150 and 300 Iraqi soldiers were reportedly killed after attacking the U.S. 7th Cavalry with rocket-propelled grenades near Najaf, 150 km south of Baghdad. No U.S. casualties were reported.
• The Pentagon is reportedly probing accounts that some U.S. soldiers captured early in the conflict were executed as they raised their hands in surrender.

March toward Baghdad

Despite fierce sandstorms sweeping across the region, U.S.-led forces are expected to continue their march towards the capital and an expected showdown with Republican Guard units.

CNN reported earlier that a column of about 1,000 Iraqi armoured vehicles were streaming out of Baghdad toward the southern Iraqi city of Najaf, where the U.S. 7th Cavalry, along with the U.S. Army's 3rd Infantry Division and U.S. Marines are said to be massing. The city was the scene of an earlier battle.

The network later said that top U.S. military officials in Washington and Central Command headquarters in Qatar said they could find no evidence of such an operation.

MacKenzie told CTV News it is unlikely the Iraqis -- reportedly from the heavily armoured Medina Divison of the elite Republican Guard -- will go into combat with U.S. troops.

"I don't think they are going to move down to make contact," MacKenzie said. "I think they are reinforcing their troops of the Medina division who have been hammered by air strikes."

At the same time, British official said a column of 70 to 120 Iraqi armoured vehicles poured out of the southern city of Basra, heading southeast in what reconnaissance intelligence said appeared to be an offensive charge.

Iraqi Information Minister Mohammed Saeed al-Sahaf said his countrymen were prepared for a battle over control of Baghdad. He said Iraqis "await surprises on how the American game of 'shock and awe' will fail."

There are reports the Iraqi regime has wired many of the bridges around Baghdad for destruction.

U.S. Central Command's Vincent Brooks said he had heard reports of the rigged bridges and added, "I'm not at all surprised by that." He gave no indication of how the possibility could affect plans to enter the Iraqi capital.

U.S. Col. (Ret.) John Caldwell says when and if the troops reach Baghdad, they'll encounter a number of "complicating factors."

"Not only do you have the three-dimensional battle space with many buildings, where snipers can hit at people from windows, ... but what you also have in urban environment is a mix of combatants and as we've seen, the Iraqis' use of non-combatants and the use of soldiers in civilian clothes," Caldwell told Canada AM Wednesday.

"All those factors make fighting in the urban environment very, very complex and it's a difficult process for all the forces to handle."

The Pentagon acknowledged Wednesday for the first time that it may have underestimated the strength of Fighters of the Fedayeen Saddam, one of Iraq's most feared paramilitary groups. "We may have underestimated that they were dispersed to so many places across Iraq to enforce regime discipline," the Pentagon official said.

In diplomatic news, British Prime Minister Tony Blair travels to the U.S. Wednesday to discuss the war in Iraq with George Bush. Blair is expected to push for significant UN involvement in Iraq when the fighting stops.

Blasts hit marketplace

Scorched corpses, mangled cars and rubble from broken buildings lay strewn around the marketplace in the Shaab area of Baghdad after "something" hit the area. If a U.S. missile or bomb was the cause, it would be the first known strike to cause substantial civilian casualties.

The Pentagon is downplaying claims that U.S. forces had launched missiles at the marketplace, where at least 15 were killed and 30 others injured.

Officials said it didn't target the district, but left open the possibility it was an errant bomb or missile.

"Is there a potential for an errant missile to go astray like a Tomahawk or something like that? Yes," a defense official, speaking on condition of anonymity, told reporters.

Earlier, Pentagon officials said they did not know the cause of the explosions and were investigating.

"Coalition forces did not target any marketplace nor were any missiles or bombs dropped in the region" that was struck Wednesday, said Maj. Gen. Stanley McChrystal at a Pentagon news briefing Wednesday. But he admits "something" landed in the area.

McChrystal said it would have been anti-aircraft artillery or a surface-to-air missile that missed its target and fell back into the marketplace.

"We don't know for a fact whether it was U.S. or Iraqi. And we can't make any assumption on either at this point," said McChrystal. "We'll continue to look and see if we missed anything."

Victoria Clarke, a Pentagon spokeswoman, told the briefing that U.S. forces struck at military targets in Baghdad, but said that the Iraqi regime puts civilians at risk by locating such targets within residential areas.

"Our objective in this campaign is to end the Iraqi regime with as few casualties as possible," said Clarke. "We go to extraordinary efforts to achieve that, including an incredible targeting process.

"Any casualty that occurs, any death that occurs, is a direct result of Saddam Hussein's policies," she added.

A series of explosions could be heard across Baghdad Wednesday afternoon, as U.S. forces lobbed at least 40 Tomahawk cruise missiles at the Iraqi capital. The strikes knocked Iraq's satellite TV signal off the air for about eight hours and also targeted government communications and satellite links, according to U.S. military officials.

Smoke was seen rising from the information ministry and the Iraqi TV building.

"These targets are key regime command-and-control assets," said Jim Wilkinson, a spokesman for U.S. Central Command.

Amnesty International says bombing the television channel could be a breach of the Geneva Conventions. Amnesty says it's a civilian object, and thus protected under international humanitarian law, but U.S. Central Command says the facility was being used to give orders to troops.

Other developments:

• Bush rallied troops at MacDill Air Force Base in Florida, saying: "The path we are taking is not easy and it may be long, yet we know our destination. We will stay on the path all the way to Baghdad and all the way to victory."
• The first convoy of food and water rolled into the port town of Umm Qasr.
• Mohammed Aldouri, Iraq's UN ambassador, accused the U.S. and Britain of inflicting thousands of casualties on this country, saying Iraq is "being subjected to a criminal, barbaric American-British military aggression."
• UN Secretary-General Kofi Annan urged the five permanent Security Council members -- the U.S., Britain, France, Russia and China -- to "overcome their differences."
• Al-Jazeera broadcast pictures of two dead soldiers and two prisoners of war, all said to be British. The television network said it obtained the video following fighting at Zubayr, near Basra.
• A second U.S. soldier has died following the grenade attack by another American soldier last Sunday at a base in Kuwait.
• The U.S. says about 500 Iraqi fighters have been killed in the last two days as troops swept through southern Iraq.
  Russia repeated denials of U.S. allegations that it is selling anti-tank guided missiles, jamming devices and night-vision goggles to Iraq.
• Iraq urged Arab leaders to hinder war by stopping oil exports, closing airspace and territorial waters to U.S. and U.K.

With reports from The Associated Press