Afghan President Hamid Karzai suspects the United States may have backed insurgent-style attacks to undermine his government but has no evidence to support his theory, the Washington Post reported Tuesday.

Karzai, whose relations with Washington have steadily deteriorated over the years, has compiled a list of dozens of attacks that he believes the US government may have been involved in, the Post wrote, citing unnamed Afghan officials.

Karzai even harbors suspicions that the Americans may have been behind a deadly attack this month on a Lebanese restaurant frequented by foreigners in Kabul, the newspaper said, quoting a presidential palace official.

However, the Afghan official acknowledged that the government had no concrete proof of a US role in any of the attacks.

The Taliban often claims responsibility for bombings employing homemade explosives and other assaults, including the recent attack on the Lebanese restaurant.

In Kabul, Afghan officials were unavailable to comment on the report.

US officials privately scoffed at the allegations, while lawmakers vented their frustration.

"I think we have to get beyond Karzai," Senator Carl Levin, chairman of the powerful Senate Armed Services Committee, told reporters.

Senate Republican Kelly Ayotte told The Hill newspaper she remains "deeply concerned that he's almost becoming delusional in terms of what the US role is there."

The United States paved the way for Karzai's coming to power by toppling the Taliban regime in 2001 over its support of Al-Qaeda.

Washington and its NATO allies have since poured billions of dollars of aid into Afghanistan and sent tens of thousands of troops to the country to battle the Taliban.

Karzai himself has admitted accepting regular deliveries of cash from the Central Intelligence Agency.

The Afghan leader has long railed against US and NATO military operations that have left Afghan civilians dead but it remains unclear why the mercurial president would try to pin blame on the Americans for attacks associated with insurgents.

Karzai has held up a crucial bilateral security agreement (BSA) negotiated with Washington that would allow for a smaller contingent of American troops to stay in the country after the end of the year.

NATO combat troops are due to withdraw by December and without a legal agreement, the United States and NATO would have to drop the idea of a post-2014 force.

"It's outrageous what Karzai is trying to do," Republican Senator John McCain, who visited Kabul this month and urged the Afghan leader to sign a BSA, told CNN.

He and Levin argued for waiting until after the April 5 election, when a new Afghan president might be more willing to strike a deal on US troops.

"We'll make the arrangements then, which means an enduring presence and not a date for withdrawal because we've seen what happened in Iraq," McCain said, referring to increased insurgent activity after Obama pulled US forces out of Iraq.

Karzai's suspicions of a conspiracy may offer an explanation why he has refused to sign the security accord, the Post wrote.

It also was possible Karzai wanted to demonstrate he was no puppet of Washington or that he wanted to persuade the Taliban he was ready for reconciliation talks.

The revelation is sure to exacerbate the already strained ties between Karzai and his American counterparts, who have long complained about his mood swings and lack of gratitude for American and NATO sacrifices.

A former US ambassador to Afghanistan, Karl Eikenberry, wrote in a 2010 diplomatic cable to Washington that Karzai "continues to shun responsibility for any sovereign burden" and cited the Afghan president's lack of reliability as a reason not to send more US troops to the country.