NATO'S mission in Afghanistan was undermined after its jets blasted two fuel tankers hijacked by the Taleban in northern Afghanistan, setting off a huge fireball Friday that killed up to 90 people, including dozens of civilians. The NATO command said only that a “large number of insurgents” were killed or injured in the pre-dawn attack near the village of Omar Khel in the once-calm province of Kunduz. But in Brussels, NATO Secretary-General Anders Fogh Rasmussen conceded civilians may have died in the airstrike. Kunduz Gov. Mohammad Omar said 90 people were killed, while a senior Afghan police officer, speaking on condition of anonymity, said that included about 40 civilians who were siphoning fuel from the trucks. “Targeting civilians is unacceptable for us,” Afghan President Hamid Karzai said, ordering an investigation. Taleban spokesman Zabiullah Mujahid said insurgents hijacked the trucks as they were headed from Tajikistan to supply NATO forces in Kabul. When the hijackers tried to drive the trucks across the Kunduz River, the vehicles became stuck in the mud and the insurgents opened valves to release fuel and lighten the loads. He said villagers swarmed the trucks to collect the fuel despite warnings that they might be hit with an airstrike. Kunduz Gov. Omar said that the Taleban killed two drivers and that the bullet-riddled body of one of them had been found. A German officer who led two platoons to the site for an investigation found the hulks of the two tankers “completely burned out.” But he said Afghan soldiers had removed the human remains. Britain and the United States defended their strategy in Afghanistan amid mounting criticism over the rising death toll from war-weary voters. But European governments warned that the NATO attack risked undermining the alliance's mission as they endorsed a swift inquiry into the bombing. Britain's Foreign Minister David Miliband said that an inquiry into the bombing, which has already been pledged by NATO Secretary General Anders Fogh Rasmussen, needed to be conducted swiftly. Swedish Foreign Minister Carl Bildt, whose country holds the EU presidency, said all deaths in Afghanistan “are regrettable.” British Prime Minister Gordon Brown, in a speech delivered at the International Institute of Strategic Studies (IISS), said: “People ask what success in Afghanistan would look like. The answer is that we will have succeeded when our troops are coming home because the Afghans are doing the job themselves.” His message was however clouded by the resignation late Thursday of Eric Joyce, a parliamentary aide to Defense Secretary Bob Ainsworth, who warned there were problems in Afghanistan “which need fixing with the greatest urgency.” US Defense Secretary Robert Gates insisted that the war was not “slipping through the administration's fingers,” but admitted: “There is a limited time for us to show that this is working.”