Kabul - A suicide bomber targeted a NATO-led military base in southern Afghanistan on Thursday, killing two US soldiers, military officials said.

The attack came as President Hamid Karzai said Afghan security forces should be able to take over the country's security from international troops in five years.

Around an hour after Karzai was sworn-in for a second term, the bomber detonated his explosives-laden vehicle at a US military base at Shahjoy in the southern province of Zabul, said provincial police chief Abdul Rahman Sarjang.

"Two US service members were killed in the attack," a US military spokesman in Kabul told the German Press Agency dpa. He was unable to provide more details of the attack.

The Taliban took responsibility for the bombing. in a statement posted on the rebels' website, claiming that 22 NATO soldiers were killed when one of their bombers, Mohammad Hashim, targeted the base.

The latest fatalities took to 292 the number of US troops killed in Afghanistan since January this year. More than 470 foreign soldiers have died in 2009, the deadliest year so far for the more than 100,000 international troops in the country.

There are around 68,000 US troops in Afghanistan, but as the Taliban-led insurgency continued to escalate, the top US general in Afghanistan has called for up to 40,000 extra troops. US President Barack Obama is in the final stages of consulting with his security advisers on whether to send tens of thousands of additional troops.

With NATO military deaths on the rise in the drawn-out conflict, public support for the presence of NATO forces is waning in Western countries, forcing the leaders there to consider an exit strategy.

During his Asian tour, Obama told CNN that his goal is to conclude the war in Afghanistan by the end of his presidency.

"I'm confident that at the end of this process, I'm going to be able to present to the American people in very clear terms what exactly is at stake, what we intend to do, how we're going to succeed, how much it's going to cost, how long it's going to take," Obama said on terlevision, talking of his new war strategy for Afghanistan.

Karzai, meanwhile, said his country's security forces would be able to take the lead in anti-insurgent operations in the most volatile regions within three years.

"I hope that by next five years, the Afghan forces are capable of taking the lead in ensuring security and stability across the country," he said during his inaugural speech in an event in Kabul, attended by nearly 1,000 people, among them about 250 international guests.

Karzai, who faces daunting challenges during his five-year term, called on Taliban militants to come back to mainstream life and renounce violence.

"We welcome all those countrymen, who are not linked to international terrorist networks, and who want to have a peaceful life in the light of our constitution. We will extend necessary assistance to them," he said.

The Taliban in the past have repeatedly said that they consider Karzai to be a puppet of the West, vowing to continue their war against the Kabul government until they force out the international troops from Afghanistan.

Karzai was named president in the country's fraud-marred polls after his main challenger, Abdullah Abdullah, pulled out of a runoff scheduled for November 7. (dpa)