A Pakistani surgeon recruited by the CIA to help find Osama bin Laden was Wednesday sentenced to 33 years in prison for treason, sparking a warning from US senators over American aid.

Shakeel Afridi, who was sacked as a government doctor two months ago, was found guilty under the tribal justice system of Khyber district, part of Pakistan's semi-autonomous tribal belt.

In addition to his jail sentence, he was fined 320,000 rupees ($3,500). The doctor had worked for years as a surgeon in lawless Khyber, part of the Taliban and Al-Qaeda infested tribal belt.

Afridi was not present in the court and was not given a chance to defend himself, officials said. Under the tribal system, he would not have had access to a lawyer.

"He has been sentenced for 33 years on treason charges and has been moved to Peshawar central jail after the verdict was announced by the local court," said Mohammad Siddiq, spokesman for the administrative head of Khyber.

But the United States rejected the charge of treason and top US senators demanded Afridi be pardoned and freed "immediately", saying the decision could put US financial assistance at risk.

"Anyone who supported the United States in finding Osama bin Laden was not working against Pakistan, they were working against Al-Qaeda," Pentagon press secretary George Little told reporters in Washington.

Carl Levin and John McCain, the top senators from the two major US parties on the Senate Armed Services Committee, in a joint statement called Afridi's sentence "shocking and outrageous."

"What Dr. Afridi did is the furthest thing from treason. It was a courageous, heroic and patriotic act which helped to locate the most wanted terrorist in the world -- a mass murderer who had the blood of many innocent Pakistanis on his hands," the two senators said.

The United States has provided Pakistan with more than $18 billion in assistance since the September 11, 2001 attacks, but US officials have persistently worried that some elements of the Pakistani establishment have maintained support for extremists.

In January, Defense Secretary Leon Panetta confirmed Afridi had worked for US intelligence by collecting DNA to verify bin Laden's presence and expressed concern about Pakistan's treatment of him.

The surgeon was arrested shortly after US troops killed the Al-Qaeda leader on May 2, 2011 and in October a Pakistani commission recommended that he be tried for treason.

Panetta said he believed someone in authority in Pakistan knew where bin Laden was hiding and as a result Islamabad was not warned about the raid.

Pakistan reacted furiously to what it called a violation of its sovereignty. It insisted it knew nothing about bin Laden's whereabouts and the operation severely damaged relations with the United States.

Afridi's trial took place over several days under assistant political agent Nasir Khan in Khyber. The verdict was confirmed by his boss, the political agent, in the northwestern city of Peshawar, the officials told AFP.

Under Pakistan's tribal justice system, Afridi has the right to appeal.

Critics said Wednesday that he should not have been tried under tribal law in the tribal belt for an alleged crime that took place outside their jurisdiction.

British newspaper The Guardian reported last July that Afridi set up a fake vaccination programme in the hope of obtaining DNA samples from those living in the house where the CIA suspected bin Laden was living to see if they were his relatives.

The United States was not 100 percent sure that the Al-Qaeda chief was living in the Abbottabad house when President Barack Obama gave the approval for Navy SEALs to raid the compound on May 2.