WASHINGTON: Pakistan for years secretly approved of US drone attacks on its territory despite public denunciations, The Washington Post reported Wednesday, citing secret documents.

The purported evidence of Islamabad's involvement came as Prime Minister Nawaz Sharif visited the White House and urged an end to the attacks, which are widely unpopular with the Pakistani public.

Pakistani support for drone attacks has long been widely suspected, although strikes reported by the Post involved several years up to 2011 -- before a slowdown in strikes and Sharif's election in May.

The newspaper said that top-secret documents and Pakistani diplomatic memos showed that the Central Intelligence Agency had drafted documents to share information on drone attacks with Pakistan.

The report by the Washington post comes just days after a separate UN report suggested that there was “strong evidence” that top Pakistani military and intelligence officials approved US drone strikes on Pakistani soil during 2004 and 2008.

At least 65 drone strikes were marked for discussion with Pakistan, including through briefings at its embassy in Washington and in materials sent physically to senior officials in Islamabad.

In one case in 2010, a document describes hitting a location “at the request of your government.” Another file referred to a joint effort at picking targets.

The article -- co-written by Bob Woodward, one of the two journalists who broke the Watergate scandal in the 1970s -- said that the documents also showed that the United States raised concerns that extremists were linked to Pakistan's powerful intelligence service.

In one incident, then secretary of state Hillary Clinton confronted Pakistan about cell phones and written materials from dead bodies of militants that showed links to the Inter-Services Intelligence agency.

In turn, a Pakistani memo gave the names of 36 US citizens believed to be CIA agents and urged the embassy in Washington not to issue visas to them, the newspaper said.

The report came a day after Amnesty International said that the United States may have broken international law by killing civilians with drones.

It pointed to an October 2012 attack that killed a 68-year-old grandmother as she picked vegetables. For the first six months of 2011, 152 combatants were killed, according to a table cited by the Post that did not list any civilian casualties.

The Obama administration has defended drone strikes as a better way to avoid civilian casualties, saying that it carefully selects Al-Qaeda-linked extremists in lawless parts of Pakistan.