KABUL, Afghanistan — A suicide bomber perched on the back of a motorcycle killed seven people, including four Afghan policemen, in an attack Saturday in the increasingly violent northern province of Kunduz, a government spokesman said.

Sixteen other people were injured in the midday attack in the provincial capital, also called Kunduz, provincial spokesman Mahbubullah Sayedi said.

The city is a major transportation hub and lies along a crucial supply line for coalition forces that has been repeatedly attacked by Taliban insurgents, who have also stepped up attacks on police and civilians in the province in an apparent attempt to destabilize local authorities and spread their insurgency beyond their strongholds in the country's south.

Pictures from the scene of Saturday's bombing showed officers loading the back of a police pickup truck with bodies of the victims, including a boy who appeared to be in his early teens. The body of the suicide bomber lay beside the mangled wreckage of his motorcycle, while windows in nearby shops and cars were shattered by the blast.

While there was no immediate sign of a connection, the bombing came on the first anniversary of a NATO warplane attack on two fuel trucks just outside Kunduz city that killed as many as 142 people, the single largest loss of civilian lives since the 2001 U.S. invasion of the country. Afghan officials repeatedly warn that such incidents undermine the central government in Kabul and fuel support for its Taliban opponents.

Also Saturday, NATO announced the capture of a Taliban commander and the killing of six insurgents in a raid on a rebel hide-out in the northern province of Takhar.

The attack followed a string of recent raids on militant leaders that aim to demoralize the insurgency and sever contacts between rebel groups.

NATO said a joint Afghan-NATO force was fired on as it approached a compound Friday where the Taliban commander was hiding. The force returned fire with the backing of coalition aircraft, then evacuated the compound and detained the commander and one of his assistants, it said.

Takhar, which neighbours Kunduz to the east, had been relatively quiet amid rising violence across Afghanistan, but recent incidents point to growing insurgent activity in the province, about 150 miles (250 kilometres) north of Kabul along the border with Tajikistan.

NATO says an airstrike in the province on Thursday killed about a dozen insurgents, but President Hamid Karzai and other Afghans said the victims were campaign workers seeking votes ahead of this month's parliamentary elections.

Farther south in Kandahar province, where much of the current fighting is focused, a Taliban commander in the provincial capital and six associates were detained in a raid Thursday, NATO said. Other Taliban leaders in rural Kandahar and the southern provinces of Paktiya and Helmand were also captured, it said.

Separately, Helmand's provincial government reported at least 12 insurgents were killed in fighting and air raids in the province on Thursday.

NATO has been intensifying its efforts with the addition of 30,000 more U.S. troops along with additional special forces soldiers who conduct most of the targeted raids alongside the Afghan army and police.

Some 140,000 foreign troops are now in the country, tasked both with driving the Taliban from areas it has held sway in for years, and ensuring security for the Sept. 18 elections that many hope will help set Afghanistan on a path to greater political stability.

So far, the election campaign has been disrupted by periodic but not paralyzing violence, with at least three candidates and five campaign workers killed in attacks. Along with the Taliban, rival candidates are also believed to be involved in some of the violence and intimidation.

On Friday, U.S. Defence Secretary Robert Gates toured U.S. bases and met with troops in Kandahar, saying he saw and heard evidence that the counterinsurgency strategy is taking hold in the Taliban's spiritual heartland.

Such progress is crucial ahead of a U.S. assessment of Afghanistan strategy in December that could determine the direction of future efforts. President Barack Obama has pledged to begin pulling out at least some troops starting next July.

Meanwhile, nervous Afghans on Saturday continued pulling funds out of the nation's largest bank despite assurances from government leaders that their money was safe.

Crowds gathered at Kabul Bank branches around the capital to withdraw dollar and Afghan currency savings, with customers saying they had lost faith in the bank's solvency following a change in leadership and reports that tens of millions of dollars had been lent to political elites for risky real estate investments.

While there was little apparent sign of panic, the deputy commander of the international coalition in Afghanistan said contingency plans were being drawn up in case of unrest sparked by a run on the bank.

"We're prepared to deal with the unexpected," Lt. Gen. Sir Nick Parker said.