WASHINGTON (Reuters) - The United States plans to keep using an airstrip inside Pakistan for non-lethal drone flights against militants near the Afghanistan border despite demands from some Pakistani officials that Washington vacate the base, three US officials said. The airstrip at Shamsi in Balochistan will continue to be used for some drone surveillance operations, while the CIA, which is principally responsible for the missions, is already using facilities in Afghanistan to launch some armed drone aircraft strikes on targets over the border in Pakistan. The facility remains fully operational and supports American counterterrorism operations in Pakistan, one of the officials told Reuters on Monday. But the official added: If, for whatever reason, it was no longer available, there are certainly other ways to continue the programme and to sustain the intense pressure its put on al Qaeda and its militant allies. The Washington Post reported on Saturday that three months ago the CIA had suspended using the base as a launch site for armed drones targeting al Qaeda and other militants. However, a US official said any temporary lull in drone operations from the Pakistani base was part of a wider dropoff instituted by the United States during bilateral tensions over Pakistans arrest and detention of CIA contractor Raymond Davis on murder charges. US officials said CIA and Pakistani personnel remain stationed at the Shamsi facility. Keeping the base open for US drone flights and maintaining Pakistani involvement in base operations is regarded in Washington as a means of ensuring that Islamabad retains a stake in the CIAs use of the remotely controlled drones. The two US officials said the United States already has adequate infrastructure outside Pakistan - principally in Afghanistan, though one official said ships could also be used - to continue substantial drone operations against militant targets in Pakistan. On Sunday, Prime Minister Syed Yousuf Raza Gilani was quoted saying that his government had never allowed the United States to use Pakistani bases for lethal drone strikes. Defence Minister Chaudhry Ahmed Mukhtar last week said Pakistan had asked the US to vacate the Shamsi base. US officials deny both of those assertions.