Taliban fighters have stormed an Afghan army outpost in the eastern Kunar province, killing 21 soldiers and kidnapping seven, the defence minister and officials have said.

Abdul Ghani Musamem, spokesman for the provincial governor, told the Reuters news agency that the attack happened early on Sunday in Ghaziabad district, a remote and mountainous area of Kunar near the border with Pakistan.

Musamem said Afghan forces had launched an operation to try to free the soldiers captured by the Taliban but police and army sources in Kunar later told Al Jazeera the fighting had stopped.

In a statement provided to media organisations, the Taliban claimed responsibility for the attack.

Afghan President Hamid Karzai postponed a planned trip to Sri Lanka over the killing of the soldiers, and Defence Minister Zahir Azmi condemned the attack and confirmed the 21 deaths in a tweet.

Prisoner swap delayed

The attack came as the Taliban suspended talks over a possible exchange of Taliban and US prisoners due to what it called the "complexity" of the situation in Afghanistan.

"The leadership of the Islamic Emirate has decided to suspend the issue for some time," Taliban spokesman Zabihullah Mujahid said in an email to media organisations, using the name the Taliban gave their 1996-2001 government.

"Therefore, the prisoner exchange process has been delayed until further notice," Mujahid said.

He provided no further detail on why the decision had been made.

In an effort to foster peace talks to end the war, US officials recently revived discussions with Taliban representatives about the proposed swap of five Taliban detainees held at Guantanamo Bay in exchange for the return of Bowe Bergdahl, a US soldier who went missing in Afghanistan in 2009, and is believed to be held by Taliban-linked fighters in northwest Pakistan.