DOHA (REUTERS) - US Secretary of State Antony Blinken said on Tuesday (Sept 7) that the United States is working to ensure charter flights carrying American citizens and at-risk Afghans can leave Afghanistan safely.

He said that the US had been conducting diplomacy with the Taliban group, which seized power in Afghanistan last month, and that Taliban officials had told Washington they will let people with travel documents freely depart Afghanistan.

Blinken denied reports that the Taliban had blocked Americans attempting to fly out of of a northern Afghan city, but said the group had not allowed charter flights to depart because some people lacked valid travel documents.

Reports have emerged over the past few days that 1,000 people, including Americans, had been stuck at Mazar-i-Sharif airport for days awaiting clearance for their charter flights to leave.

One organiser blamed the delay on the State Department - criticism echoed by Republicans who have said not enough has been done to facilitate the charter flights.

Blinken was speaking at a news conference in Qatar, a US ally that has emerged as a key interlocutor to the Taliban, which seized power in Kabul on Aug. 15 after the Western-backed government collapsed.

Blinken said Washington had identified a "relatively" small number of Americans seeking to depart from Mazar-i-Sharif. But one of the main challenges around the charter flights attempting to depart was that some people lacked the valid travel documents which effectively blocked the departure of the entire group, he said.

"And it's my understanding is that the Taliban has not denied exit to anyone holding a valid document, but they have said those without valid documents, at this point, can't leave," Blinken said. "Because all of these people are grouped together, that's meant that flights have not been allowed to go," he said.

Blinken and US Secretary of Defence Lloyd Austin are in Qatar to meet their counterparts regarding the evacuation of Americans and Afghans at risk following the Taliban takeover and to build a consensus among allies on how to respond to the movement.

They thanked Qatar for its support and actions.

"Qatar went above and beyond, and your generosity saved thousands of lives," Austin said at a joint press conference in Doha.

Qatar's Foreign Minister Mohammed bin Abdulrahman Al-Thani said his country hoped that Kabul airport would be up and running for passengers in the next few days, but that no agreement on how to run it had yet been reached.

Qatar has been working with Turkey and the US on restoring operations at Kabul airport. Sheikh Mohammed said the airport will require an upgrade in equipment.