KABUL: Investigations were under way Sunday into the deaths of seven soldiers and police killed in what Afghan officials called a mis-targeted NATO air strike, one of the worst "friendly fire" incidents of an eight-year war.

It occurred while NATO and Afghan forces, searching for two missing American paratroopers in a barren, rugged area, clashed with Taliban insurgents on Friday, they said. "The investigation continues," defence ministry spokesman General Mohammad Zahir Azimi told AFP. "We and NATO are investigating the incident." Azimi said four army soldiers and three police officers were killed in the air strike which was called in to help troops fighting rebels in remote Badghis province of western Afghanistan. "We know that they were killed in the air strike. We're currently investigating the incident to find out why they were hit so such incidents can be prevented in the future," he added. Zemarai Bashary, a spokesman for the interior ministry, which handles police matters, also said the probe was ongoing. "We're part of the investigation. It's a joint investigation between NATO, interior and defence ministries," the spokesman added. He refused to give details. Azimi said NATO troops who were fighting the rebels alongside the Afghans also suffered casualties but he refused to give figures. NATO's International Security Assistance Force (ISAF) said its personnel and Afghan forces had been "engaged by enemy forces," meaning the Taliban, while searching for two soldiers who went missing Wednesday while trying to recover airdropped supplies from a river. It said the 25 were "killed or wounded during a joint operation that involved multiple engagements over several hours." It added that four Afghan soldiers and three police were killed. Earlier it said five of the wounded were US soldiers. The alliance force said it was "currently investigating whether some of the casualties were caused by ISAF close air support." However, one Western military official, speaking on condition of anonymity, told AFP it appeared to be a "blue-on-blue incident" -- a military term for friendly fire -- with "a huge number of casualties". If proven, Friday's incident will have been one of the deadliest of its kind. Nine Afghan police lost their lives in July last year when NATO fighter planes mistakenly bombed them in the southwestern province of Farah. The use of air power in Afghanistan has been controversial, with civilian casualties sparking public anger and prompting President Hamid Karzai to demand a halt to air strikes earlier this year. On Friday, German Defence Minister Karl-Theodor zu Guttenberg said mistakes had been made in a German-ordered air raid in September, carried out by US aircraft, which killed as many as 142 people. More than 100,000 troops under NATO and US command are in Afghanistan fighting a Taliban insurgency now at its deadliest in the eight years since US-led troops toppled the Islamist regime. US President Barack Obama is considering a request from military commanders to boost troop numbers by up to 40,000. Last week, French Foreign Minister Bernard Kouchner hinted at strains on the alliance, hitting out at the United States and Germany for failing to coordinate on NATO policy and branding Afghan President Hamid Karzai "corrupt". Separately, the Afghan army said a five-day operation that ended on Friday in the northern province of Kunduz resulted in the deaths of 133 militants. The Afghan army also said at least three Afghan soldiers and more than a dozen Taliban militants were killed on Saturday in southern Afghanistan.