An unusually powerful United States delegation has arrived in Pakistan to deliver the warning that the United States would act unilaterally, if necessary, to attack extremist groups that use the country as a haven to kill Americans, according to a senior American official. US Secretary of State Hillary Clinton, Central Intelligence Agency Director David Petraeus and General Martin E Dempsey, the new chairman of the Joint Chiefs of Staff, planned to push their Pakistani counterparts to make a definitive choice between fighting terrorists or supporting them, The New York Times quoted the administration official, as saying. "This is a time for clarity," Clinton declared in Kabul, where she met Afghan President Hamid Karzai before leaving for Islamabad. "No one should be in any way mistaken about allowing this to continue without paying a very big price." "There's no place to go any longer," Clinton added, referring to Pakistan's leaders, whom the administration has accused of equivocating by supporting the Afghan insurgency. The American and Pakistani officials, who included the Pakistan Army chief General Ashfaq Parvez Kayani, and the Inter-Services Intelligence Director General Lt Gen. Ahmed Shuja Pasha, met for four hours, ending after 2 am, the report said. A senior administration official said afterward that both sides had agreed to keep talking on Friday and did not want to comment in the meantime, said the report, adding that according to a Pakistani official, Petraeus met separately with Pasha. Earlier, another senior Pakistani official said that Clinton's remarks in Kabul did not "enable the atmosphere." Her comments, however, underscored a growing American realisation that hopes for a smooth troops withdrawal from Afghanistan by 2014 now hinged on Pakistan's willingness to confront insurgent groups based in the country who have had the support of Pakistan's intelligence service. According to the report, before the meeting, which took place at the residence of Prime Minister Yousaf Raza Gilani, a senior administration official said that the delegation would make it clear that if the Pakistanis did not act against insurgents like the Haqqani network, then the US would have to.