For years, American officials have tried to persuade Pakistan’s military chiefs and prime ministers to cooperate with U.S.-led war plans in neighboring Afghanistan.

But now it is a politician in a far-flung province who is standing in the way.

Angered by U.S. drone strikes, Imran Khan has effectively halted NATO convoys through northwest Pakistan, a vital crossing point for trucks carrying supplies to and from landlocked Afghanistan.

Khan, an Oxford-educated millionaire and former cricket star, has no real power in the national government. But his party controls the local government in Khyber Pakhtunkhwa province, which NATO convoys must pass through to reach the northern border crossing.

After U.S. drone strikes in Pakistan this fall, the 61-year-old politician called on his supporters to block the transit routes in protest. Prime Minister Nawaz Sharif’s government has appeared powerless to stop him.

With Sharif and Pakistan’s military vowing that the supply routes must remain open, Khan’s campaign is a remarkable show of defiance in a country that has been under military rule for more than half of its 67-year history.

A self-described liberal pacifist who became more attuned to his Muslim faith after his globe-trotting cricket career ended, Khan shows no sign of backing down. He says that although U.S. drone strikes may be aimed at violent militants, many wind up killing innocent civilians and fuel terrorism by angering the local population.

“The reason we are taking this stand is to tell the U.S., ‘Okay, it’s fine to protect American lives, but how can you sacrifice a whole country for it?’ ” Khan said in a recent interview at his mountaintop estate on the outskirts of Islamabad.

The attacks also violate Pakistan’s sovereignty, Khan says, and he notes that the Pakistani army is bearing the brunt of the retaliatory strikes from Islamist militants.

But Khan is drawing fierce criticism from some Pakistanis who accuse him of using the issue for political gain. Khan, a member of Parliament, unsuccessfully sought the prime minister’s job in elections last year.

Rifaat S. Hussain, a defense and political analyst in Islamabad, said Khan has become a “one-man show” who “has yet to mature into a statesman.”

“Many of us had hoped, now that elections are over, he would have focused on local issues, corruption, law and order, terrorism, but instead he is trying to play to the peanut gallery,” Hussain said.

Honing his focus

Khan ended his two-decade-long cricket career in 1992, after leading Pakistan’s national team to its only World Cup victory. He then became a philanthropist and founded his party, Tehreek-e-Insaf (PTI), or Movement for Justice.

Though it struggled for years to win seats in Parliament, Khan emerged as a leading contender in Pakistan’s national elections.

He became a media sensation because of his perceived appeal to progressive younger voters and urbanites, tens of thousands of whom would show up at his campaign rallies. His past reputation as a playboy — as well as his marriage to and divorce from socialite Jemima Goldsmith, daughter of British billionaire James Goldsmith — added to his mystique.

But Khan’s party finished third in the elections.

Khan had been warning for months that he and his party would seek to cut off NATO supply routes if the U.S. drone strikes didn’t end. The U.S. military says the land routes, used by civilian contractors, are a quick and cost-effective way to remove its vast store of equipment and hardware from landlocked Afghanistan ahead of the departure of most troops next year.

When the drone attacks continued this fall, including a November strike in Kyber Pakhtunkhwa, Khan and thousands of others held a day-long protest on a highway used by NATO convoys on the outskirts of the province’s capital, Peshawar. The following day, Nov. 24, his party’s political and municipal workers erected checkpoints to search and turn back trucks suspected of carrying NATO supplies.

When reports reached Kabul and Washington that some NATO truck drivers were being roughed up by protesters, the coalition suspended its convoys through the northern border crossing.

Coalition military commanders in Kabul and U.S. Embassy officials in Islamabad have sought to play down the disruption, noting that NATO supplies are still moving through Pakistan’s southern province of Baluchistan.

But Khan’s party says it also has plans to blockade the port in the southern Pakistani city of Karachi, which would be a dramatic escalation. And there are growing signs that U.S. and NATO officials consider Khan’s stance to be far more than just an annoyance.

When U.S. Defense Secretary Chuck Hagel visited Pakistan in early December, he warned that the country could lose billions of dollars in U.S. military aid if the blockade continued, according to U.S. and Pakistani media accounts. Two weeks later, Marine Gen. Joseph F. Dunford Jr., commander of coalition forces in Afghanistan, traveled to Islamabad to meet with Pakistan’s new military chief, Lt. Gen. Raheel Sharif.

In a blunt signal of the coalition’s unease, about 20 diplomats from NATO countries, including the United States, summoned Khan for dinner in early December at the German ambassador’s residence in Islamabad. According to Khan and others present, the encounter became tense.

“They kept saying, ‘Look, we have nothing to do with it; it’s all the CIA’ ” carrying out the drone attacks, Khan recalled. “I said, ‘Look, you are all coalition partners.’ ”

At one point, Khan said, he asked the European diplomats how they would feel if Pakistan started secretly killing people living in their countries who were wanted on warrants in Pakistan.

Critics in government

Sharif’s government is starting to increase its criticism of Khan, who is also holding a series of demonstrations against Sharif’s economic policies and rising inflation.

Information Minister Pervez Rasheed accused Khan of being a demagogue “trying to divert the attention of people from his failures” in his province.

“It is the right of every individual to protest, but the way PTI has blocked NATO supplies, it will create problems for the country at an international level,” Rasheed said in an interview.

Even some conservative religious politicians question Khan’s strategy.

“He is providing an excuse to the U.S. to remain on Afghanistan’s soil,” said Abdul Jalil Jan, a leader of the Jamiat Ulema-e-Islam-Sami party in Kyber Pakhunkhwa.

But on a recent visit by a reporter to protest camps near Peshawar, party workers chanted “Long live Imran Khan” as they waited to quiz the next round of truck drivers on their cargo.

Haq Nawaz Khan in Peshawar, Shaiq Hussain in Islamabad and Craig Whitlock in Washington contributed to this report.