President Ashraf Ghani and his rival Abdullah Abdullah signed an agreement on Sunday to end a bitter feud that had plunged the country into political crisis for months.

"I welcome the decision taken by Afghanistan's political leaders to resolve their differences and join efforts to form an inclusive government," Stoltenberg said in a statement.

The breakthrough comes as Afghanistan battles a rapid spread of coronavirus and surging militant violence that saw dozens killed in brutal attacks last week.

"In the midst of the COVID-19 pandemic and continued Taliban violence against their fellow Afghans, it is more important than ever that all Afghan leaders unite and work towards enduring peace in Afghanistan," Stoltenberg said.

"All parties should seize this unprecedented opportunity for peace."

Under the agreement, Abdullah will lead future peace talks with the Taliban, who have already signed a landmark accord with Washington to pave the way for the withdrawal of foreign forces -- including NATO's training mission -- from Afghanistan.

But the chances of peace are uncertain, with fighting still raging between the Taliban and Afghan forces in the provinces.

NATO ended combat operations in Afghanistan at the end of 2014 but maintains a 16,000-strong mission to train, advise and support local forces.