Bonn: Afghan President Hamid Karzai has accused Pakistan, which is boycotting an international conference on Afghanistan starting from Monday in Bonn, of undermining all negotiations with the Taliban.

"Up until now, they have sadly refused to back efforts for negotiations with the Taliban," Karzai told Der Spiegel weekly in comments reported in German and due to be published on Monday.

The Bonn meeting will seek to chart a course for Afghanistan after the NATO withdrawal in 2014, but a boycott by Pakistan has dealt a blow to already fragile hopes for a roadmap.

Pakistan is seen as vital to any prospect of stability in the war-ravaged country a decade after US-led forces ousted the Taliban, who had offered safe haven to Al-Qaeda leader Osama bin Laden.

But Islamabad pulled out after 24 Pakistani soldiers were killed in cross-border NATO air strikes a week ago, although sources close to the German foreign ministry said it would be kept informed of progress at the conference.

 The United States has voiced regret over the strikes but has stopped short of issuing an apology while the American military conducts an investigation.

US Secretary of State Hillary Clinton yesterday called Pakistan's prime minister to offer condolences.

In the call with Yousuf Raza Gilani, Clinton, "reiterated America's respect for Pakistan's sovereignty and commitment to working together in pursuit of shared objectives on the basis of mutual interest and mutual respect," the State Department said.

Islamabad has so far refused to take part in the US investigation into the incident, exacerbating fears of a prolonged crisis between Pakistan and the United States.