A White House official travelled to Damascus earlier this year for secret meetings with the Syrian government seeking the release of at least two US citizens.
A Trump administration official speaking on condition of anonymity has named the envoy as top White House counterterrorism advisor Kash Patel, saying he had flown to Damascus.
"It is emblematic of how President Trump has made it a major priority to bring Americans home who have been detained overseas," said the official on Sunday, who was confirming a report in the Wall Street Journal.
The White House and State Department have not responded to requests for comment.
The newspaper, citing Trump administration officials and others familiar with negotiations, described Patel's trip as the first time such a high-level US official had met in Syria with the isolated government of Syrian President Bashar al-Assad in more than a decade.
Syria erupted into civil war nearly a decade ago after Assad in 2011 began a brutal crackdown on protesters calling for an end to his family's rule.
The newspaper said US officials hoped a deal with Assad could free Austin Tice, a journalist and former Marine officer who disappeared while reporting in Syria in 2012, and Majd Kamalmaz, a Syrian-American therapist who disappeared after being stopped at a Syrian government checkpoint in 2017.
At least four other Americans are believed to be held by the Syrian government, the newspaper reported, but little is known about those cases.
The Journal reported Trump wrote Assad a private letter in March, proposing a "direct dialogue" about Tice.
It said Lebanon's top security chief, Abbas Ibrahim, met last week at the White House with national security adviser Robert O'Brien to discuss the Americans held in Syria.
Talks with Syria have not gotten very far, according to people briefed on them, the newspaper reported, saying Damascus has repeatedly demanded Washington withdraw all its forces from the country.