Taliban attackers wearing U.S. uniforms mounted simultaneous predawn raids on two NATO bases in Afghanistan Saturday, part of an apparent new strategy by insurgents to spread their attacks across the country.

While U.S. and coalition forces focus their resources on battles in and around the Taliban's birthplace in the south, including Kandahar province where the bulk of Canadian troops are based, the insurgents are stepping up activity in the north and east.

Saturday's attacks on forward bases in eastern Khowst province, near the Pakistan border, were driven off by NATO and Afghan government troops and at least 20 of the insurgents were killed and five more captured, according to Western and Afghan officials said.

Three more insurgents, including a commander, were killed in an airstrike as they fled the area.

NATO reported no casualties, but the Afghan Interior Ministry said two of its soldiers were killed and three were wounded.

The attacks began at about 4 a.m. and lasted several hours and were aimed at Forward Operating Base Salerno, the main coalition base in Khowst province, as well as an adjacent installation known as Camp Chapman. Chapman was the scene of a suicide bombing last December that killed seven CIA staff.

Two of the attackers managed to penetrate the perimeter at Salerno, but were killed immediately, the NATO force said.

Khowst police chief Abdul Hakim Ishaqzai said the insurgents were armed with rocket-propelled grenades, mortars and suicide vests. He said Afghan and Western forces seized a number of weapons and two vehicles packed with explosives.

He said about 50 Taliban took part in the two assaults and after being driven away from the bases, approached the nearby offices of the provincial governor and police headquarters.

He said they were scattered from those sites as well. "Given the size of the enemy's force, this could have been a major catastrophe for Khost. Luckily we prevented it."

Small-arms fire continued through the morning, while NATO helicopters patrolled overhead.

The dead attackers were wearing U.S. Army uniforms, which can be easily purchased in shops in Kabul and other large Afghan cities, possibly pilfered from military warehouses.

U.S. and Afghan officials blamed the attack on the Haqqani network, a Pakistan-based faction of the Taliban with close ties to al Qaeda.

The attacks appeared to be part of a growing pattern of insurgent assaults far from the battles in Kandahar and Helmand provinces, which have been the main focus of the NATO campaign.

In the last four months, Taliban fighters have carried out strikes against large, heavily fortified air bases at Kandahar; Jalalabad in the east; and Bagram, north of Kabul.

The rash of coordinated attacks on major installations, none of which were at all successful, represents a departure from the insurgents' usual hit-and-run ambushes.

Such frontal assaults were formerly a rarity because of the near impossibility of the insurgents overrunning well-armed bases of that size.

But late Friday, insurgents stormed a police checkpoint in Takhar province near the northern border with Tajikistan. The day before, Taliban fighters killed eight Afghan policemen in a raid on a checkpoint outside the northern city of Kunduz.

And on Wednesday, an Afghan police driver with family links to the Taliban killed three Spaniards -- two police trainers and their interpreter -- at a training centre in the northern province of Badghis.

Although the Afghan capital is relatively secure, incidents apparently directed at female students have raised concern about Taliban intimidation within the city.

The Health Ministry said 48 pupils and teachers at the Zabihullah Esmati High School were rushed to hospitals Saturday after falling ill with breathing problems and nausea. All but nine were treated and released after blood samples were taken to try to determine the cause.

On Wednesday, dozens of students and teachers at another Kabul girls' school became sick when an unknown gas spread through classrooms, education officials said. The cause of that incident has not been determined, but officials fear the apparent poisonings could be part of an insurgent campaign to frighten girls from attending school.

Also Saturday, three more American service members were killed -- two in a bombing in the south and the third in fighting in eastern Afghanistan, the U.S. command said. That brought to 38 the number of U.S. troops killed this month -- well below last month's figure of 66.

With files from The Associated Press