The official, who spoke on condition of anonymity, named the official as Kash Patel, a deputy assistant to President Donald Trump and the top White House counterterrorism official, 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, who was confirming a report in the Wall Street Journal.
The White House and the State Department did not immediately respond to requests for comment.
The newspaper, citing Trump administration officials and others familiar with the negotiations, described Patel's trip as the first time such a high-level US official has met in Syria with the isolated Assad government in more than a decade.
The United States suspended operations at the US embassy in Damascus in February 2012 after demonstrations against Assad in 2011 began a brutal crackdown on protesters calling for an end to his regime, leading to Syria's bloody civil war.The newspaper said US officials hope a deal with Assad would lead to freedom for Austin Tice, a freelance 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 that Trump wrote Assad a private letter in March, proposing a "direct dialog" about Tice.
It said that 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, according to people involved in the talks.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.