Washington's ambassador to Kabul said Thursday no deadline exists for withdrawing US troops from Afghanistan and recommitted the US to helping build the capacity and competence of Afghan security forces. US forces would begin a “gradual and responsible transition” in July 2011 conditional on the readiness of Afghanistan's own police and army to take over the security of their war-battered country, Karl Eikenberry said. “US combat forces will start to return from Afghanistan in July 2011. It is not a deadline, despite what some in both the United States and Afghanistan have said,” he told a gathering of senior Afghan officials and mostly Western diplomats. “Our troops will begin a gradual and responsible transition in 2011, taking into account the conditions on the ground and Afghanistan's ability to handle its security requirements,” he said. US President Barack Obama has pledged an extra 30,000 troops to bolster the 71,000 already fighting a Taliban-led insurgency that has become more virulent and deadly over the past year. In a major speech unveiling a new fast-track war strategy, Obama said the surge would see troops in Afghanistan “seize the initiative” to end the unpopular war and begin pulling out in July 2011. It was the first time Obama had said US forces would start returning home after 18 months, as he groped for an exit from a conflict many backers see as similar to Vietnam. The date has been seized on as a deadline for US withdrawal, though Eikenberry was eager to dispel the impression the US had set an exit date. US troops serve with forces from more than 40 NATO countries, which together total more than 113,000. NATO members have pledged up to 7,000 more troops between them, bringing the surge to 37,000. US aide wanted Karzai replaced A senior United Nations official has said his former deputy wanted to seek US support to force Afghan President Hamid Karzai from office, the New York Times reported Thursday. The Times said Kai Eide, the top UN official in Afghanistan, accused his American deputy Peter Galbraith of wanting to undertake “a secret mission to Washington” to garner support for Karzai's ouster. The allegations are the latest twist to emerge from the diplomatic wrangling surrounding fraud-tainted presidential elections in Afghanistan last August. As allegations of fraud became too numerous to ignore, the UN and Western nations began to lose hope that the vote could give the Kabul government a stamp of legitimacy and wondered how best to proceed. Galbraith, who left Afghanistan abruptly in early September and was fired weeks later, said he was forced out after disagreeing with Eide on how to handle the fallout.