Representative Eliot Engel, the chairman of the House Foreign Affairs Committee, issued a subpoena to force Zalmay Khalilzad to appear on September 19.

The legally-binding order came days after President Donald Trump said diplomacy with the Taliban was "dead" and offered the bombshell revelation that he had arranged but canceled talks with the Islamist militants at the Camp David presidential retreat.

In the committee's first subpoena since the Democrats won back Congress, Engel said the Trump administration had stalled for months on lawmakers' requests to know more about the Taliban talks.

"More than 2,000 American troops have died in Afghanistan, and I'm fed up with this administration keeping Congress and the American people in the dark on the peace process and how we're going to bring this long war to a close," Engel said in a statement.

"We need to hear directly from the administration's point person on Afghanistan to understand how this process went off the rails," he said.

A subpoena from Congress compels an official to appear, although the Trump administration has taken the unusual stance of defying subpoenas, setting up legal battles.

The State Department did not immediately comment on whether Khalilzad intended to comply as ordered.

Khalilzad held nine rounds of talks with the Taliban in Doha, saying little as negotiations went on behind closed doors.

He later said he had reached an agreement in principle with the Taliban in which the United States would pull out troops and the militants would promise to break with Al-Qaeda.

Trump has been eager to end America's longest war, launched 18 years ago after the September 11 attacks.

But he accused the Taliban of bad faith for launching an attack in Kabul that killed a US solider on the eve of the purported Kabul talks.

State Department spokeswoman Morgan Ortagus said Wednesday that Khalilzad remained on the job and had returned to Washington but that Taliban talks were off in accordance with Trump's declarations.