Pakistan is holding firm to its boycott of the Bonn international conference on Afghanistan, and warns it will stay away from any future peace process unless its sovereignty and security concerns are better respected.

With Pakistan conspicuously absent from Monday's international conference in Bonn, U.S. Ambassador to Pakistan Cameron Munter went on domestic TV here in Islamabad to express Washington's disappointment.

"Afghanistan is Pakistan's neighbor. Pakistan deserves a voice at the table to talk about these things. We have tried to convince our Pakistani friends to attend. If they choose not to attend, that is their choice," said Munter.

Pakistani officials announced a boycott of the Bonn conference soon after U.S. helicopters and fighter jets reportedly fired on two Pakistani military encampments, killing 24 soldiers. Pakistan resisted all efforts to persuade it to send envoys to the conference, including a phone call Sunday, on the eve of the conference, to Pakistani President Asif Ali Zardari from President Barack Obama, who expressed regret over the incident.

Ambassador Munter said Monday the United States is complying with a Pakistan's order to vacate U.S. personnel from an airbase in southwestern Pakistan. He repeated the White House's message that last week's attack was a "tragedy" and a "mistake." In an interview with Pakistan state television, he hinted that those responsible may face punishment.

"I can only say that we will have an investigation, and that if people have been found to have made mistakes, there will be results," he said.

Pakistani leaders says they are fully reviewing the terms for the country's engagement with the United States. Abdul Basit, a spokesman for the Foreign Ministry in Islamabad, said Pakistan supports Afghan peace efforts, but that last month's NATO attack created circumstances that would not permit Pakistan to attend the Bonn conference. He said if those circumstances do not change, it will be difficult for Pakistan to associate itself with any peace process in Afghanistan.

Pakistan's main demand is for better coordination between its military and the U.S.-led NATO stabilization force in Afghanistan to ensure that Pakistani sovereignty is respected.