ISLAMABAD - The US Ambassador to Islamabad phoned Washington with an urgent plea: Stop an imminent CIA drone strike against militants on the Pakistani side of the Afghan border, reported American media on Tuesday. He feared the timing of the attack would further damage ties with Islamabad, coming only a day after the government grudgingly freed a CIA contractor held for weeks for killing two Pakistanis. Munters rare request was forwarded to the head of the CIA, who dismissed it. US officials said Leon Panettas decision was driven by anger at Pakistan for imprisoning Raymond Davis for so long and a belief that the militants being targeted were too important to pass up. The deadly March 17 attack helped send the US-Pakistan relationship into a tailspin from which it has not recovered. The attacks have also strained the relationship between the US State Department and the CIA, where officials argue that killing militants who threaten US interests should take priority over political considerations, said US officials. That tension was clearly visible between Ambassador Munter and the CIA station chief in Islamabad, who recently left his post because of illness, said a senior Western official in the region. When the doors are closed they are shouting at each other, but once the doors are open they are congenial in front of the embassy staff, said the official. The hard-charging station chief also clashed with the ISI chief over drone strikes, said a Pakistani official. The CIA does not comment on the drone programme. A US official familiar with the issue played down the tension. It is very, very rare for the chief of mission to express concern about any particular operation, the official said, referring to the ambassador. When concerns are raised, theyre always given close consideration. Munter must sign off on every planned drone attack in Pakistan, although he rarely voices an objection, said a former aide to the ambassador. If Munter disagrees with a planned strike, the CIA director can appeal to him, said two US officials, providing the most detailed description of the process to date. Clinton can also weigh in, and has done so at least once, one US official said. On March 17, Munter used the embassys secure line in an attempt to stop an imminent drone strike. His concern was that the strike - a day after the release of the CIA contractor Davis - would set back Washingtons already shaky relations with Islamabad, said the former aide and a senior US official. Munters request went to the State Department and was forwarded to then-CIA director Panetta, now secretary of defence, who insisted on going ahead, said the officials. It is unclear whether Clinton was involved in the decision. Two pairs of missiles were fired three minutes apart, hitting several dozen tribesmen meeting in the open in Shiga village near the Afghan border. Pakistani officials and local tribesmen said four Taliban fighters and 38 innocent people were killed. In a rare public statement, Army Chief General Ashfaq Parvez Kayani, said the jirga was carelessly and callously targeted with complete disregard to human life. US intelligence officials brusquely dismissed the Pakistani claims. ISI chief Lt-Gen Ahmed Shuja Pasha took the strike as a personal insult because he had stepped in to get Davis released, Pakistani officials said. The strike hampered counterterrorism cooperation between the CIA and the ISI, and the Pakistani government started sending US military trainers home - a process that accelerated after the raid that killed bin Laden. Pasha made a personal trip to Washington in April in an attempt to repair relations. The ISI chief said he would work to let in more CIA operatives if the US would consider including Pakistan in the process of drone strike targeting, said US officials at the time. But before Pasha had returned home, two US missile strikes killed six suspected Taliban fighters in the South Waziristan tribal area. Pakistani officials said the attacks were seen as another slap to Pasha and made it impossible for him to raise the CIAs requests with the army or the govt. This pattern continued after the US raid that killed bin Laden in the Pakistani town of Abbottabad on May 2. The operation outraged the Pakistani government because it was not told about it beforehand. Kerry, chairman of the Senate Foreign Relations Committee, visited in mid-May trying to salvage the relationship. He made some progress but just as he left on May 16, the CIA launched a missile strike in North Waziristan, killing seven suspected militants. In response, Kayani and President Zardari sent Kerry angry messages that he received when he touched down in Dubai, said Kerrys spokeswoman Jennifer Berlin, confirming details that first appeared in The New York Times Magazine. The prevailing view at the State Department and the White House is that CIA strikes are motivated by a drive to kill as many militants as possible in what the US sees as a window of opportunity that might soon close, rather than a deliberate attempt to torpedo diplomacy, said the official.