The US envoy negotiating with the Taliban hailed “significant progress” on Saturday in finding a solution to end Afghanistan's long-running war.

“Meetings here were more productive than they have been in the past. We made significant progress on vital issues,” Zalmay Khalilzad, the US special representative for Afghan reconciliation, tweeted after six days of talks with the Taliban in Qatar.

The envoy has, however, added: "We have a number of issues left to work out. Nothing is agreed until everything is agreed, and “everything” must include an intra-Afghan dialogue and comprehensive ceasefire."

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He said he was flying back to Afghanistan to discuss the talks.

While he did not give further details, floated proposals include a withdrawal by the United States of its troops in return for Taliban guarantees not to shelter foreign extremists — the initial reason for the US intervention.

President Donald Trump has been eager to end America's longest war, which was launched shortly after the September 11, 2001 attacks.

Trump has already said he will pull half of the 14,000 US troops from Afghanistan.

Meanwhile, Voice of America (VOA) reported that the United States and the Taliban have likely reached an agreement for withdrawal of American forces from Afghanistan.

"In return, the insurgent group has given assurances that no international terrorist groups would be allowed to use Afghan soil to threaten America or any other country in future," the radio broadcaster added.

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Taliban sources told VOA that it is expected the formal announcement for the withdrawal plan may come as early as Saturday and latest by Monday, if things go according to plan.

The plan would require the Taliban to observe a ceasefire. However, both the withdrawal and the cease-fire will be “limited and conditional”, according to VOA.

Sources added that the possibility cannot be ruled out that Trump announces the plan during his State of the Union speech since now the government shut down has ended.