KABUL (AFP) - A Nato air strike killed up to 27 Afghan civilians, including women and a child, sparking fresh anger from Kabul on Monday against US-led forces pressing a major offensive to defeat the Taliban. In a further blow to efforts to quell the eight-year insurgency, a suicide bomber killed an influential Afghan leader and 14 other people in a relatively peaceful eastern province on the Pakistan border Monday, the Afghan Interior Ministry said. Top US commander Stanley McChrystal, who has made winning Afghan hearts and minds the focus of plans to end the increasingly costly war, was forced into another apology over civilian deaths after the third incident in a week. We are extremely saddened by the tragic loss of innocent lives, he said. I have made it clear to our forces that we are here to protect the Afghan people, and inadvertently killing or injuring civilians undermines their trust and confidence in our mission, McChrystal added in a statement. A statement from President Hamid Karzai said McChrystal had visited him at his palace on Sunday to personally apologise for deaths. McChrystal and his superior, General David Petraeus, mapped out an offensive lasting 12-18 months that would strike beyond the current focus of operations in the southern province of Helmand. The government said four women and a child were among the civilians killed in Gujran district of Daykundi province on Sunday when Nato forces mistook their convoy for Taliban militants. A statement from the council of ministers, chaired by Karzai, condemned the incident as unjustifiable, saying that 27 people were killed and 12 wounded. But the enormity of the challenging in reversing the Taliban insurgency was underlined Monday when a suicide bomber strapped with explosives walked up to a tribal gathering in eastern province Nangarhar and killed a key tribal elder. As a result of a suicide attack at 3:45pm (11.15 GMT) today, 15 people were martyred and 20 were wounded, the Interior Ministry said in a statement. Police spokesman Col Abdul Ghafour told AFP the dead included influential tribal leader Mohammad Zaman Ghamsharik, a former jihadi commander during the fight to evict Soviet troops in the 1980s. Nato on Monday described resistance from Taliban fighters as determined in Marjah, on the ninth day of the offensive, but spoke of cautious optimism in nearby Nad Ali, as early signs indicate a return to normality.