ABOARD A US MILITARY AIRCRAFT: The top US military officer on Wednesday strongly rejected accusations from Pakistan that Nato deliberately killed 24 Pakistani soldiers last weekend.

General Martin Dempsey, chairman of the US military's Joint Chiefs of Staff, told Reuters that he was trying to discuss the incident with Pakistan behind closed doors.

“Candidly we don't want to try to resolve this issue through the media. No offense,” he said in an interview as he flew back to Washington after a trip to London.

“The one thing I will say publicly and categorically is that this was not a deliberate attack.”

In comments widely published in Pakistani media on Wednesday, Pakistan's director general of military operations, Major General Ishfaq Nadeem, described the Nato cross-border attack as a deliberate, blatant act of aggression.

Dempsey declined to discuss details of the US military's review into the incident, but questioned Nadeem's logic.

“What in the world would we gain by attacking a Pakistan border post?,” Dempsey asked.

Nadeem said the Nato helicopters appeared near the post around 15 to 20 minutes past midnight, opened fire, then left about 45 minutes later. They reappeared at 0115 local time and attacked again for another hour.

Dempsey said the military was pouring over its own data from the incident.

“We're in the process of reviewing radio traffic, gun tapes, all of the things that an investigation has to consider before I can really make any statement about the duration,” Dempsey said.

“But I can say, categorically, it was not a deliberate attack.”

Without acknowledging the use of drones at the Shamsi Air Base, Dempsey confirmed a report by Reuters on Tuesday that preparations were already underway to leave the facility.

“We've been told to leave so we have to prepare to leave. And you know, we're doing the calculations on what the airlift (will need to be) to take the equipment out of there,” he said.

Dempsey played down the operational impact of the moves during his trip to London this week, saying the US military had tactical alternatives.

“What I'm really concerned about is the deterioration of the relationship with Pakistan long-term, not its immediate effect on any tactical actions,” Dempsey said.

On Capitol Hill, Senators Carl Levin and John McCain expressed their condolences on the Senate floor on Wednesday to families of Pakistanis who died in the border incident.

But the Senate also approved an amendment instructing the Pentagon to assess how much money has been paid to Pakistan over the last decade as reimbursement for fighting extremists - and to look at ways of reducing or terminating the payments as the United States withdraws from Afghanistan.

The amendment by Senator Bob Corker must still be approved by the House of Representatives before it can become law.