More than 100 Taliban fighters overran an Afghan army base Sunday, killing at least 19 soldiers in the bloodiest attack on the country’s armed forces in many months.

Also Sunday, the Taliban said it would postpone negotiations with the United States over the release of Army Sgt. Bowe Bergdahl, who has been held captive since 2009.

In Sunday’s assault, a mass of insurgents surrounded a small base in the remote Ghaziabad district of Konar province early in the morning, according to Gen. Abdul Habib, Konar’s police chief. He said the militants were carrying guns and rocket-propelled grenades.

“It was a savage attack by the enemies of Afghanistan,” Habib said.

As of Sunday afternoon, Afghan forces had retaken the outpost.

Winter is typically a time of relative peace in Afghanistan, when Taliban leaders return to Pakistan. But this year, the insurgency appears to have stepped up its attacks in an effort to disrupt presidential elections scheduled for April. Ghaziabad, along the Afghan-Pakistani border, is one of the country’s most restive districts and is thought to be home to several al-Qaeda fighters.

Small Afghan army outposts in southern and eastern Afghanistan have always been vulnerable to large-scale Taliban attacks, particularly as the U.S. military has reduced its presence. Still, bloody strikes of this scale, in which the Taliban is able to successfully overrun an outpost, ­have been rare.

In a sign of the attack’s importance, Afghan President Hamid Karzai postponed an official trip to Sri Lanka. In a statement condemning the raid, Karzai’s palace asked Pakistan’s leadership to “realistically and seriously” cooperate with Afghanistan in the fight against militancy.

The strike in Konar came “amid preparations by security forces for launching an attack to clear the Taliban threat from the area,” said Col. Bahwul Khan, a police officer in the province.

In addition to the 19 dead, three Afghan soldiers are missing. “We do not know whether they have fled or have helped the Taliban to launch the attack,” Habib said.

Bergdahl, who was captured in June 2009, is the only U.S. service member known to be held hostage in the Afghan war.

For two years, the United States has expressed interest in the possibility of a prisoner exchange involving five detainees at Guantanamo Bay, Cuba, for Bergdahl.

“Given the complexity of the political situation in the country, the leadership council of the Emirate has decided to postpone this matter for some time. Therefore, the process of exchange of prisoners is delayed until further order,” the Taliban said in a statement e-mailed to journalists Sunday, referring to the organization’s alternate name, the Islamic Emirate of Afghanistan.

In recent months, U.S. officials have attempted to resuscitate negotiations by offering the simultaneous release of the five Afghan detainees. The Taliban statement said that “progress was made through the mediation to some extent.” But the statement didn’t specify any advances or explain when the progress occurred.

U.S. officials have never acknowledged any steps forward in negotiations, raising questions about whether the Taliban statement marks any substantive change in relations.

The Taliban statement did not explain the specific reasons for the postponement of negotiations.