US and Taliban negotiators held talks in Doha on Monday as potentially decisive dialogue to enable Washington to drawdown its deployment to Afghanistan stretched into the night.

The fourth day of the ninth round of dialogue, which continued until after 20:30 GMT, saw Taliban and US representatives shuttling between the two sides' negotiating teams clutching papers, an AFP correspondent said.

The insurgent group had earlier said that it was finalizing technical points of an agreement with Washington at the talks being held in an up-market members' club to end 18 years of war.

"We will defend Afghan forces now and after any agreement with the Talibs," the US chief negotiator Zalmay Khalilzad tweeted Monday in response to suggestions a deal might not apply to the insurgents' fight against the US-backed Afghan government.

He also tweeted that all sides in the negotiations had agreed "Afghanistan's future will be determined in intra-Afghan negotiations."

The four pillars of any deal are expected to be foreign troop withdrawal, a cease-fire, counter-terror guarantees, and intra-Afghan dialogue. 

Any agreement would be announced before the media as well as representatives from neighboring countries and China, Russia, and the United Nations, the Taliban has said. 

The Taliban's spokesperson in Doha Suhail Shaheen tweeted that the foes would reconvene talks on Tuesday to "try to finalize the final points of the agreement."

The US, which invaded Afghanistan and toppled the Taliban from power in 2001 after the September 11 attacks, wants to withdraw thousands of troops but only in return for the group renouncing Al Qaeda and curbing attacks.

Washington is hoping to strike an agreement with the Taliban by September 1 - ahead of Afghan polls due the same month, and US presidential polls next year.

The Doha talks are being held against a backdrop of persistent violence in Afghanistan.