Talks between five nations held in Turkmenistan, with war in neighbouring Afghanistan topping their agenda.
An Afghan air force pilot has been killed in a bomb blast in Kabul, claimed by the Taliban, officials said.
The pilot, Hamidullah Azimi, died on Saturday when a sticky bomb attached to his vehicle detonated, officials said, adding that five civilians were wounded in the explosion.
Azimi was trained to fly US-made UH-60 Black Hawk helicopters and had served with the Afghan air force for almost four years, the forces’ commander, Abdul Fatah Eshaqzai, told the Reuters news agency.
He had moved to Kabul with his family a year ago due to security threats, Eshaqzai added.
Taliban spokesman Zabihullah Mujahid claimed the attack in a statement.
Reuters was first to detail a Taliban campaign to assassinate pilots off-base that Afghan officials say killed at least seven Afghan pilots before Saturday’s killing.
The Taliban has confirmed a programme that would see US-trained Afghan pilots “targeted and eliminated”.
US and Afghan officials believe it is a deliberate effort to destroy Afghanistan’s corps of US- and NATO-trained military pilots as fighting escalates across the country.
The Taliban – which has no air force – wants to level the playing field as they press major ground offensives that have seen them swiftly seize territory since May.
Emboldened by Washington’s announcement that it was ending its military mission by the end of August, the Taliban has launched a military blitz across the country which has gained momentum in recent days.
On Friday, the Taliban captured its first provincial capital in years when it took control of Zaranj, on the border with Iran in Afghanistan’s southern Nimruz province.
On Saturday the Taliban captured the city of Sheberghan, the city’s deputy governor told the AFP news agency.
Qader Malia, the deputy governor of Sheberghan in Jawzjan province that government forces and officials had retreated to the airport on the outskirts of the northern Afghan city, where they were preparing to defend themselves.
As the Taliban eyes other cities, the Afghan air force has played a crucial role in holding it back.
Azimi’s death came just days after the Special Inspector General for Afghan Reconstruction (SIGAR), in a report to the US Congress, said the targeting of pilots detailed by Reuters was another “worrisome development” for the Afghan air force as it reels from a surge in fighting.
In its quarterly report covering the quarter through June, SIGAR described an air force increasingly under strain and becoming less ready to fight.
Its fleet of UH-60 Black Hawk helicopters had a 39 percent readiness rate in June, about half the level of April and May.
“All aircraft platforms are overtaxed due to increased requests for close air support, intelligence, surveillance, reconnaissance missions and aerial resupply now that the [Afghan military] largely lacks US air support,” the report said.