Pakistani authorities are increasingly monitoring and restricting the movements of foreigners working in this country, according to U.S. and international aid officials, some of whom said they believe the changes represent a backlash against U.S. actions in Pakistan that have enraged the government and the public.

The added restraints include four police refusals to allow U.S. Embassy employees to enter the volatile northwestern city of Peshawar over the past 10 days. Embassy officials said the employees were making routine trips to attend meetings or to fill in for workers at the U.S. Consulate there. Those incidents came after months of what international aid organizations said are growing requirements for federal permits to travel in areas that had been easily accessible, as well as deportations of workers whose visas have expired while their extension applications languished in bureaucracy.

The widely publicized episodes in Peshawar threaten to become another flash point in a frayed bilateral relationship that U.S. officials had hoped was improving, after fatal shootings by a CIA contractor and the U.S. commando raid that killed Osama bin Laden. International aid groups say the fallout from those incidents, which sparked debate about the presence of Americans in Pakistan, has prompted scrutiny of all foreigners that could imperil humanitarian work in zones recovering from conflict and floods.

“It has the potential to cause serious delays, especially because some of this donor money is time-sensitive and emergency-related,” said Jack Byrne, country representative for Catholic Relief Services and chairman of an umbrella group of international humanitarian organizations in Pakistan.

The heightened restrictions mostly apply in the northwest region bordering the militant-riddled tribal belt, and several Pakistani officials said they are designed to ensure foreigners’ safety. But security in Peshawar and its province has generally improved in the past year, and one provincial official said the restrictions also reflect concerns that foreigners have too much latitude in Pakistan.

That sentiment has grown since CIA contractor Raymond A. Davis was arrested after killing two Pakistanis in January, sparking a diplomatic row.

“That incident shook the mutual trust of both governments. We don’t want a repeat,” said the provincial official, Information Minister Mian Iftikhar Hussain. “In no country are the foreign diplomats freely roaming without informing the government. But when we do this, there is a hue and cry.”

In each of the recent incidents, U.S. officials said the embassy followed a long-standing routine of notifying Peshawar police that employees were driving from the capital, Islamabad, so police could escort them from a highway tollbooth into the city.

On those occasions, the employees were turned away at the tollbooth for lacking permits known as “No Objection Certificates,” or NOCs, which are issued by the federal Interior Ministry but can also involve approvals from the military or intelligence agencies.

U.S. officials said that those permits had not been required before and that there has long been an agreement that diplomats can travel between embassy and consular posts without them, in part because obtaining NOCs can take more than a week.

Security and government officials in northwest Pakistan countered that the requirement has always existed and that it applies to all foreigners.

U.S. officials said they were unsure whether the Peshawar incidents amounted to a systematic effort to thwart the movements of Americans — whose consulate in the city is widely viewed here as a front for CIA operations — or whether they were done for show. Each time U.S. vehicles were turned away from tollbooths, television cameras were there.

Whatever the reason, a U.S. official said, “to us, this is not a constructive way to rebuild the relationship.”

Officials at Pakistan’s Foreign and Interior ministries did not respond to numerous calls for comment.

Foreigners, particularly Americans, have long faced scrutiny in Pakistan. In 2009, U.S. officials complained about what they described as harassment, including vehicle searches and visa delays so extreme that sections of the embassy were barely staffed.

Those delays were mostly resolved as relations warmed last year. But the alliance foundered again following the Davis incident, after which Pakistani intelligence vowed to crack down on what they described as a network of CIA agents roaming the nation.

This year, Pakistan expelled more than 100 U.S. Special Operations trainers. The United States responded by deciding to withhold $800 million in military aid and reimbursement. Pakistan recently approved visas for 87 CIA officers, but U.S. officials say visa extensions — to allow recently arrived diplomats to stay past 90 days — are processed so slowly that some diplomats are forced to return to Washington.

International aid organizations say the fallout from strained U.S.-Pakistan ties has extended to their employees, exacerbating what they call a “shrinking space” for humanitarian work, already hampered by insurgents. Aid officials said NOCs are required for foreigners traveling in areas where they had not been required previously, such as the Kohistan and Shangla districts in the northwest, as well as in parts of the flood zones of northern Sindh province.

Aid officials said the slow permitting process has delayed projects and led in some cases to understaffing. In one example, an American employee of Catholic Relief Services whose visa expired while he awaited an extension was jailed last month for nine days in Sindh, then deported.

Benoit de Gryse, the local mission head for Doctors Without Borders, said that in recent months, Pakistani intelligence agents have begun to “knock on our doors once a week” at project sites in the northwest. They are not hostile, he said.

The heightened suspicions were understandable after the Davis and bin Laden episodes, said Michael O’Brien, a spokesman for the International Committee of the Red Cross. But he said the restrictions could undermine the organization’s programs, particularly in Peshawar, where 80 percent of its foreign staff is based.

“The bottom line is, this is not our country,” O’Brien said. “But definitely there needs to be some balance between the work done by people to provide assistance and the arrangements to monitor where people are going.”

Special correspondent Haq Nawaz Khan in Peshawar contributed to this report.