KABUL, Afghanistan -- Afghan officials on Monday mourned the loss of 21 soldiers killed by the Taliban in the single deadliest incident for the Afghan army in at least a year, as new details emerged about the attack which threatened to further strain relations with neighboring Pakistan.
The soldiers died Sunday when hundreds of heavily armed Taliban insurgents attacked two remote army checkpoints near to each other in eastern Afghanistan's Kunar Province. Officials said that five Afghan soldiers are missing.
At the ceremony in Kabul attended by Ministry of Defense officials and families of the slain soldiers, an honor guard stood at attention behind the long line of coffins draped in the Afghan flag and topped with bouquets of flowers.
Gen. Bismullah Khan Mohammadi, Afghanistan's defense minister, stressed that the Afghan army's capacity has increased.
"We will stand against those who... come to Afghanistan to kill our people," he said.
Mohammadi appeared to be making a veiled reference to Pakistan - one of several comments that could exacerbate an already tense relationship between Kabul and Islamabad.
Kunar province borders Pakistan. Afghanistan has often accused Pakistan of aiding Taliban leaders sheltering across the border. Pakistan's relationship with the Taliban is complicated, in that it helped the group seize control of Afghanistan in 1996.
Kabul also has repeatedly accused Islamabad of providing the insurgents sanctuary on its territory following the U.S.-led invasion of Afghanistan in 2001.
While initial reports surrounding the Kunar attack were vague - there was no specific mention that they came across the border from Pakistan but it was implied by Afghan officials that they had. Afghan President Hamid Karzai also mentioned Pakistan's need to fight terrorism without making a direct link to the Kunar assault.
But officials on Monday were far more direct.
Defense ministry spokesman Gen. Mohammad Zahir Azimi said Pakistanis, Arabs, Chechens and Afghan were among the "hundreds" of insurgents involved in the attack, citing "exact information" and intelligence. He did not elaborate.
Kabul has often said it has evidence of the involvement of Chechens, Arabs and Pakistanis in Taliban attacks, without offering proof.
He said the attack was well-organized and planned outside of the country.
"The attack was planned outside of the country and hundreds of attackers crossed border and launched their attack, it was a well-organized," Azimi said.
The insurgents, "tens" of whom were killed, according to Azimi, targeted two checkpoints and blocked a main road. One insurgent detonated a suicide vest as army reinforcements tried to reach the scene, Azimi told reporters in Kabul.
He confirmed that five soldiers from the outpost are still missing and it was unclear if they are being held captive.
Sunday's attack highlighted the challenges facing Afghanistan's National Security Forces, which have been suffering mounting casualties since they took the lead from foreign troops in the war against the Taliban.
Azimi said that the Afghan army had requested air support assistance from the NATO-led coalition, but it arrived once the attack was almost over.
The Taliban - which claimed responsibility for Sunday's attack - have been ramping up attacks in recent months in attempts to take advantage of the withdrawal of foreign troops at the end of 2014. They also have vowed to disrupt the nation's April 5 election.