LONDON — Lebanon’s top intelligence official has vowed to continue his effort to secure freedom for six Americans missing in Syria despite no evidence that the Trump administration’s outreach to President Bashar al-Assad has produced results.

Maj. Gen. Abbas Ibrahim, who heads Lebanon’s General Security Directorate, spoke as he prepared to return to Beirut after a visit to Washington, at the invitation of the White House, that was marked by controversy.

The visit was aimed at advancing a tenuous negotiation with the Syrian government launched earlier this year by President Trump to seek the release of the Americans, including freelance journalist Austin Tice, a Washington Post contributor.

But it came amid differences within the administration over how far it should go in dealing with a regime ostracized since 2012 for human rights abuses. A top White House counterterrorism official, Kash Patel, made a secret visit to Damascus earlier in the year, the first official contact between the two governments since 2012, the Wall Street Journal reported this week. He was joined by U.S. Ambassador Roger Carstens, an envoy for hostage affairs, in the negotiations in Damascus, where they met with Ali Mamlouk, Syria’s top intelligence official, according to a newspaper aligned with the Syrian government.

There were also criticisms of the administration’s dealings with Ibrahim, whose position puts him in frequent contact with Hezbollah, a party in the Lebanese government that is designated as a terrorist organization by the United States.

Ibrahim, who has secured the release of multiple hostages in the Middle East over the past decade, said the politics of both the countries involved in the issue were not his concern.

“This is a humanitarian issue. I am not interfering in politics, and the politics on both sides is not my business,” he said. “I am just a mediator trying to get those people back home.”

He declined to discuss details of any exchanges between Assad’s government and Trump officials in order not to jeopardize possible progress. But he confirmed that the discussions have not yet resulted in any proof of life of Tice or the others. They include Majd Kamalmaz, a psychotherapist who went missing in 2017 after being detained at a government checkpoint, and four other U.S. citizens whose families don’t want publicity.

Other people familiar with long-standing efforts to free the Americans say the Syrian government has not even acknowledged holding them. Rather, it is insisting on a complete withdrawal of U.S. troops from Syria and the lifting of U.S. sanctions as a precondition for any further discussions, they said.

“This is not an easy case,” Ibrahim said. “First of all, we have to build a bridge of confidence between the two parties. And there is no confidence between the two parties.”

Ibrahim’s visit stirred concerns among some in Washington that Trump might be prepared to meet those conditions to pull off an American hostage release ahead of the U.S. election, said Robert Satloff, the executive director of the Washington Institute for Near East Policy.

“To link the departure of U.S. troops from Syria to the otherwise noble effort to release hostages is to mix strategic and humanitarian issues,” he said.

Secretary of State Mike Pompeo appeared to lay those concerns to rest on Wednesday, telling a news conference in Washington that the administration is “not going to change American policy” to secure the Americans’ release.

“Our ask is that the Syrians release Mr. Tice, tell us what they know. They have chosen not to do that,” he said.

Ibrahim’s past successes include securing the release of U.S. traveler Sam Goodwin, who was detained at a Syrian government checkpoint last year, and a Canadian citizen, Kristian Baxter, who had crossed illegally into Syria from Lebanon.

In 2014, Ibrahim oversaw the release of a group of nuns kidnapped by the al-Qaeda-linked Jabhat al-Nusra, and the previous year, he mediated a hostage exchange in which a group of Hezbollah-affiliated pilgrims kidnapped by Syrian rebels was traded for a Turkish airlines crew abducted in Beirut.

He has been involved for many years in the effort to locate Tice, who disappeared in 2012 during an attempt to leave the rebel-held town of Darayya, outside Damascus, which was surrounded by government troops at the time. His family has repeatedly said they are confident he is still alive.

Ibrahim’s return to Beirut was delayed by several days because he tested positive for the novel coronavirus. A second test he took on Wednesday was negative, he said, and so far no one he was in contact with in Washington is known to have tested positive.

Haidamous reported from Washington.