PESHAWAR, PAKISTAN—A Pakistani doctor who helped the U.S. track down Osama bin Laden was sentenced to 33 years in prison on Wednesday for conspiring against the state, officials said, a verdict that is likely to further strain the country's relationship with Washington.

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Shakil Afridi ran a vaccination program for the CIA to collect DNA and verify bin Laden's presence at the compound in the town of Abbottabad where U.S. commandos killed the Al Qaeda chief last May in a unilateral raid. The operation outraged Pakistani officials, who portrayed it as an act of treachery by a supposed ally.

Senior U.S. officials have called for Afridi to be released, saying his work served Pakistani and American interests. But many Pakistani officials, especially those working for the country's powerful spy agency, do not see it that way.

“He was working for a foreign spy agency. We are looking after our national interests,” said a Pakistani intelligence official, speaking on condition of anonymity in line with the agency's policy.

Afridi's conviction comes at a sensitive time because the U.S. is already frustrated by Pakistan's refusal to reopen NATO supply routes to Afghanistan. The supply routes were closed six months ago in retaliation for American airstrikes that killed 24 Pakistani soldiers.

Afridi was detained sometime after the May 2, 2011, raid, but the start of his trial was never publicized.

He was tried under the Frontier Crimes Regulations, or FCR, the set of laws that govern Pakistan's semiautonomous tribal region. Human rights organizations have criticized the FCR for not providing suspects due process of law. There is no right to legal representation, to present material evidence or cross-examine witnesses.

The verdict was handed down by a Khyber government official in consultation with a council of elders, according to Nasir Khan, a government official in the Khyber tribal area, where the doctor was arrested and tried.

As well as the prison term, Afridi was ordered to pay a fine of about $3,500 and will spend an additional three and half years in prison if he does not, Khan said.

Afridi can appeal the verdict to the FCR commissioner within a period of two months, said Iqbal Khan, another Khyber government official.

The U.S. operation that killed bin Laden severely strained ties with Pakistan. The Pakistani government kicked out U.S. military trainers and limited counterterrorism co-operation with the CIA.

The relationship got even worse in November when the U.S. killed the 24 Pakistani soldiers at two posts along the Afghan border, an attack that Washington said was an accident but the Pakistani army insisted was deliberate.

Pakistan immediately retaliated by closing the NATO supply routes and kicking the U.S. out of a base used by American drones. Before the attack, the U.S and other NATO countries fighting in Afghanistan shipped about 30 per cent of their nonlethal supplies through Pakistan. Since then, the coalition has used far more expensive routes through Russia and Central Asia.

The U.S. has pressed Pakistan to reopen the supply line, but negotiations have been hampered by Washington's refusal to apologize for the attack and stop drone strikes in the country as demanded by Pakistan's parliament. Many observers view the latter demand with skepticism because elements within Pakistan's government and military have supported the attacks in the past.

The latest drone strike took place Wednesday, when two missiles hit a compound in Datta Khel Kalai village in the North Waziristan tribal area, killing four suspected militants, said Pakistani intelligence officials, speaking on condition of anonymity because they were not authorized to talk to the media.

The U.S. does not discuss the cover CIA drone program in Pakistan in detail.

The Obama administration has expressed regret for the attack on Pakistan's troops, but is not willing to tender an apology out of concern that it could open the president up to attacks by Republicans angry at Pakistan's lack of co-operation on the Afghan war.

Despite its disagreements with the U.S., Pakistan appeared close to reopening the supply routes last week, prompting NATO to invite President Asif Ali Zardari to a major summit earlier this week in Chicago. But negotiations have faltered on Pakistan's demand for much higher transit fees, and the U.S. made its frustration clear at the summit.

President Barack Obama refused to meet one-on-one with Zardari and did not mention Pakistan in the list of countries he thanked in his speech Monday for helping get war supplies into Afghanistan.

On Tuesday, a Senate panel approved a foreign aid budget for next year that slashes U.S. assistance to Pakistan by more than half and threatens further reductions if it fails to open the NATO supply routes.

American lawmakers are also frustrated by suspicions that Pakistan is aiding militants who use its territory to attack U.S. troops in Afghanistan — allegations Islamabad has rejected. There is also lingering resentment over the fact that bin Laden was found hiding deep inside Pakistan.

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But the U.S. cannot afford to turn its back on Pakistan entirely.

Pakistan is seen as vital to negotiating a peace deal with the Afghan Taliban and their allies given the country's historical ties with the militants.

The Pakistani government is also keen to repair relations with the U.S., partly to receive over a billion dollars in American aid it needs to fill out its budget as it looks ahead to national elections scheduled for 2013. But patching up ties is politically sensitive in a country where anti-American sentiment is rampant.

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