WASHINGTON (Reuters) NATO will soon release the results of a joint probe with Pakistan into last weeks killing of three Pakistani soldiers in a cross-border incursion by Western forces, the Pentagon said on Tuesday. The September 30 helicopter strike was the most serious of recent cross-border incidents involving NATO-led forces fighting in Afghanistan, which have stoked tensions with neighbouring Pakistan. Pentagon Press Secretary Geoff Morrell said the results of the investigation would be released in the next 24 hours by the NATO-led International Security Assistance Force (ISAF) and by Pakistani authorities. He did not elaborate on the findings but appeared to play down the likelihood of any major revelations. He described the helicopter strike as a regrettable mistake. You should take a look at the investigation and see what it says. I dont think it differs, frankly - the ultimate conclusion - that much from what weve been speaking to publicly as to what happened, Morrell said. The incident occurred in Pakistans western Kurram region, when NATO forces were investigating what appeared to be a new Taliban fighting position along the border, Morrell said. I guess they came under fire while they were checking out that position, he added. About half of all non-lethal supplies for western forces in land-locked Afghanistan pass through Pakistan, giving Pakistan considerable leverage over the United States, which also needs Pakistans help in fighting insurgents. Morrell said that despite the helicopter strike, ties between the US and Pakistani militaries were very strong. Throughout this period of tension, if you will, relations - mil-to-mil relations have proceeded, Morrell said. There are two routes through Pakistan into Afghanistan. The one that Pakistan closed goes through the Khyber Pass in northwest Pakistan to the border town of Torkham and on to Kabul. US officials have said there has not been any impact on supplies to the Afghan war but hope to get the pass open quickly given its importance, particularly in delivering fuel. We really do have a sense that were making progress and this can be resolved soon, Morrell said. I would point out that it is in the Pakistanis interest to do this. I mean, this is a huge commercial enterprise for them and they do not get paid until that fuel is delivered to the point of destination in Afghanistan. Morrell said Pakistan had two military representatives taking part in the investigation, giving them full access to all the inboard cameras and video so that we could be as transparent as possible. (US Defence Secretary Robert Gates) of course, deeply regrets the incident and is very much encouraging of his staff to work closely with the Pakistani military to ensure that we are devising ways to prevent this from happening in the future, he said.