Afghan forces repulsed an assault by hundreds of militants, many fromacross the border in Pakistan, officials said Wednesday, in the biggest clashes sincethe presidential election almost four weeks ago.NATO air support was called in to help beat back the attack that left 60 militantsand at least five Afghan soldiers dead at an army base near the porous border onMonday night."A group of terrorists and foreign fighters numbering about 500... launched a bigoperation targeting army posts in Zirok district of Paktika province," the Afghandefence ministry said in a statement.It said the militants were trying to score a high-profile victory after failing to mounta significant attack on polling day despite threatening to target voters, electionofficials and security forces.The Afghan National Directorate of Security, the country's intelligence agency, said300 fighters from the Haqqani network, which is allied to the Taliban, and otherinsurgents were involved."Haqqani and foreign fighters along with suicide attackers carried out an assault onthe night of April 28 to capture a military base in Zirok district," it said."As a result of a counter-attack by government forces backed by coalition airforce,60 members of Haqqani and other foreign fighters were killed and a large numberinjured."The Haqqani network is blamed for some of the deadliest attacks in Afghanistan, including bombings of the US and Indian embassies in Kabul.A Haqqani source in Pakistan confirmed Monday's incident to AFP."Allied forces and the Afghan army retaliated to the assault and killed 60 fighters,"he said."The fighters left and took with them 40 bodies of their colleagues and 12 Afghansoldiers who were alive."The Haqqani source said the bodies of 20 militants were with the Afghans and amessage had been sent offering to exchange the captured soldiers for them.Afghan officials said only one soldier had been taken hostage.US officials have in the past accused Pakistani intelligence agencies of links to theHaqqani network, which has bases in Pakistan's tribal districts.Washington put the network on its terror blacklist in September 2012, and thePentagon said the group represented a "significant threat" to national security.Afghanistan's election is heading for a run-off on June 7 after former foreignminister Abdullah Abdullah and ex-World Bank economist Ashraf Ghani failed tosecure the 50 percent vote needed for first-round victory.A second election in June -- at the height of the traditional "fighting season" -- willpresent another major challenge for Afghanistan's stretched security forces.