A political row erupted Thursday after the Washington Post reported that US lawmakers secretly inserted language into a huge spending bill that blocks major changes to the nation's controversial drone program.

Veteran US Senator John McCain said he was flabbergasted to learn that members of the Senate and House Appropriations Committees, who are mainly focused on cobbling together funding for federal agencies, slipped a provision into the $1.1 trillion spending package that maintains the Central Intelligence Agency's role in deadly counter-terrorism operations.

"This is the making of a major policy concerning our war on terror, and it's hidden in a secret annex?" McCain told AFP, after he stepped off the Senate floor where he angrily waved a copy of the Post and complained about the secret manoeuver.

"What it requires is hearings in the Intelligence Committee and the Armed Services Committee."

President Barack Obama's administration is said to be pressing for shifting drone operations away from the CIA and under military control, amid mounting concern over drone attacks resulting in civilian casualties.

Late last month an alleged US drone strike killed two Al-Qaeda suspects in Yemen. A day earlier, the United Nations said 16 civilians were killed when two separate wedding processions were targeted by drones in the country on December 12.

McCain said he was so angered about the congressional move that he will now vote against passage of the massive bill, which lays out federal spending through September and essentially eliminates prospects of an election-year government shutdown.

"This certainly is a deciding factor for me," he said.

McCain would not say whether he supports the sort of shift in the drone program believed to be backed by Obama, but he warned of the "arrogance" of congressional appropriators making an "arbitrary decision" blocking any such move without wider input.

Number two Senate Democrat Dick Durbin, who is on the Appropriations Committee, would not confirm the Post report, saying "there are just certain areas that we can't discuss publicly, for fear that it might endanger our country."

And he declined to comment on McCain's suggestion that drone operations be debated in committee.

There is no mention of drones in the 1,582 publicly released pages of the spending bill expected to pass Congress this week.

"Adjustments to classified programs are addressed in the accompanying classified annex," the legislation notes.