Pakistani activists shout anti-India slogans during a protest in Karachi on Friday, a day after Pakistan’s parliament passed resolutions condemning provocative statements by Indian leaders. (Rizwan Tabassum/AFP/Getty Images)

After weeks of tension between Pakistan and India, the leaders of the two nuclear-armed nations took steps Tuesday to reset a relationship that is once again making U.S. officials nervous.

In a series of phone calls to the leaders of Muslim countries, ­Indian Prime Minister Narendra Modi called his counterpart in Pakistan, Nawaz Sharif, to wish him a happy Ramadan. Modi, who made Pakistani leaders furious last week when he accused the country of harboring terrorists, told Sharif he hoped they could work together to overcome historical grievances between the neighbors.

In a gesture of goodwill, Modi also told Sharif that India would release Pakistani fishermen it had detained for straying into its territorial waters, according to Modi’s office.

Sharif said Pakistan in return would release the Indian fishermen in its custody and told Modi it was time for the two countries to “forget their differences and leave behind talk of confrontation and war,” according to a summary of the call issued by Sharif’s office.

The apparently friendly tone of the call was a far cry from the bellicose language that was being used on both sides of the border last week.

After India’s military conducted an anti-terrorism mission along its eastern border with Burma, a high-level official in the Information Ministry, Rajyavardhan Rathore, was quoted as saying the operation was a “message” to other countries such as Pakistan that India will not hesitate to pursue threats beyond its borders.

Those comments rattled leaders and military commanders in Pakistan, home to several militant groups that have carried out attacks in India, including a 2008 siege in Mumbai that killed 166 people.

Modi also upset Pakistani leaders during a recent visit to Bangladesh, where he lashed out at Pakistan, calling it a regional “nuisance.”

Pakistan’s defense minister, Khawaja Muhammad Asif, suggested Monday that Pakistan would use nuclear weapons if it ever felt threatened by India.

“India must know that the Pakistani atom bomb is not for firecrackers,” he told a Pakistani television station.

In Washington, U.S. officials have been anxiously watching developments from the region. Secretary of State John F. Kerry, who is nursing a broken leg, called Sharif on Tuesday to discuss the state of relations between Pakistan and India.

“It’s of enormous concern to all of us for all the obvious reasons,” Kerry said. “These are two very important countries playing a critical role with respect to regional interests. It’s very important that there be no misinterpretation or miscalculation.”

Since India and Pakistan both formally became nuclear powers in 1998, world leaders have been worried that even a minor conflict along the volatile border could quickly escalate. India has a no-first-use policy for nuclear weapons; Pakistan has refused to take such a stance.

On Monday, the Stockholm International Peace Research Institute released a report noting that both Pakistan and India continue to expand “their nuclear weapon production capabilities” and to develop “new missile delivery systems.”

The institute, which monitors nuclear proliferation, estimates that India has between 90 and 110 nuclear warheads. Pakistan has between 100 and 120, the group said.

DeYoung reported from Washington. Annie Gowen in New Delhi contributed to this report.

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