WASHINGTON — Relentless, deadly attacks by the Taliban, including a car bombing Thursday that killed a U.S. service member, are testing President Donald Trump's resolve to withdraw troops from Afghanistan and end what he has called America's “endless” war.

The death of the American — the fourth U.S. service member killed in the past two weeks in Afghanistan — could be used to argue that it is long past time to bring U.S. troops home.

But the Afghan government and others worry that the attacks during ongoing U.S.-Taliban talks are evidence that the insurgent group cannot be trusted to end the violence and renounce international terror groups like al-Qaida and the Islamic State.

“We want to make sure we are negotiating a peace, not simply a withdrawal,” House Foreign Affairs Committee Chairman Eliot Engel said in a letter Thursday to Trump's peace envoy, Zalmay Khalilzad.

Engel is demanding that Khalilzad, who has said the U.S. and the Taliban are on the threshold of a peace deal, come to testify before the House committee about the negotiations. The envoy was invited to appear Feb. 26 and April 8, but never responded.

“I do not consider your testimony at this hearing optional,” Engel, D-N.Y., wrote in the letter.

Khalizad is now back in Doha, Qatar, where the Taliban have a political office, after updating the Afghan government on the latest developments in the talks. He said earlier this week that the insurgent group and the U.S. had reached a deal “in principle” and all that was still needed was Trump's signature, but the details have not been released.

A senior U.S. official said it's not clear how long the envoy will be in Doha or where he will go afterward. It's possible he could go back to Kabul or he could return to Washington, depending on what happens during discussions over the fine print of the potential deal with the Taliban, according to the official, who was not authorized to discuss the sensitive negotiations and spoke on condition of anonymity.

While details are scant about the deal the administration appears close to approving, the rising violence has rattled Kabul, the capital, and other sites around the country.

“Peace with a group that is still killing innocent people is meaningless,” said Afghan President Ashraf Ghani.

The attack Thursday by a Taliban suicide car bomber in Kabul killed the U.S. service member, a Romanian soldier and at least 10 Afghan civilians in a busy diplomatic area that includes the U.S. Embassy. About 42 people were wounded.

Hours later, the Taliban set off a car bomb outside an Afghan military base in a neighboring province, killing four civilians.

Those attacks followed the disclosure by Amnesty International that Abdul Samad Amiri, the Afghanistan Independent Human Rights Commission's acting director in Ghor province, was kidnapped and killed by the Taliban. And on Monday, the Taliban attacked a foreign compound, killing at least 16 people and wounding more than 100, almost all of them local civilians.

When reporters asked Defense Secretary Mark Esper on Thursday what the Taliban needed to do to show they can be trusted, Esper said it was a matter for negotiators.

“Until we see a final agreed-upon document that outlines what that agreement looks like, I'm just going to hold my tongue because what I don't want to do is get out ahead, or askew, of the sensitive negations,” Esper said while traveling in Britain.

Trump has repeatedly stated his desire to end U.S. involvement in Afghanistan, where 2,400 American troops have been killed.