Lebanese businessman and U.S. resident Nizar Zakka landed in Beirut on Tuesday after he was released by Iran following nearly four years of imprisonment, in a move the Trump administration called an encouraging sign.

Nizar Zakka in 2013. Courtesy of Friends of Nizar Zakka via AP file

Information technology consultant Nizar Zakka, 52, was arrested on his way to the Tehran airport in September 2015 after being invited by the Iranian government to attend a conference on sustainable development. He was convicted on unspecified spying charges in a closed-door trial and sentenced to ten years behind bars.

"After more than 1,350 days in captivity in Iran, we have received excellent news: Mr. Nizar Zakka is a free man," lawyer Jason Poblete said in a statement issued Tuesday morning. "Nizar looks forward to reuniting with family and friends. Nizar expresses his sincerest thanks to those who never forgot him."

After arriving in Beirut, reporters saw Zakka entering the presidential palace, dressed in a suit and tie.

Dressed in a suit and tie, Zakka said he had emerged from his detention with a renewed commitment to human rights and that media coverage had given him hope during his time behind bars.

“I love freedom and this is freedom. It's unbelievable, it's unbelievable,” Zakka said in an interview with NBC News.

Asked about his treatment in prison, Zakka said he did not want to delve into those details just as he was celebrating his freedom. “Today it's a happy day. Let's keep it a happy day.”

But Zakka said he was kept in solitary confinement for “almost a year.”

He expressed particular gratitude to Lebanese media for following his plight. “I would like to insist here, that the Lebanese media have been the only oxygen I had, by supporting me,” he told NBC News. “They supported me every single day. Every single day. And I love them.”

Zakka said he was not certain why he was released at this moment but said he believed the move could be a first step to reducing tensions between Iran and the United States, calling it “good timing.”

He said he was held with other Americans in Tehran and called on President Donald Trump to push for the release of U.S. citizens and other foreign nationals still held in Iran.

“I really wish every American would be released very soon. They deserve to be released. Extra effort by President Trump should be done ASAP.”

He said the Americans still imprisoned were “tired” and added: “Everybody’s tired. Get them home.”

Zakka, whose three children live in the United States, flew to Beirut from Tehran accompanied by the head of security in Lebanon, Maj. Gen. Ibrahim Abbas.

Earlier, Iranian judiciary spokesman Gholamhossein Esmaili said that Iran would hand Zakka over to Lebanese officials.

Zakka had been living in Washington, D.C. and has permanent U.S. residency. The U.S. government had protested his imprisonment and called for his release.

“We are encouraged by the news that Lebanese citizen Nizar Zakka has been released by the Iranian regime and hope that this is a positive sign for Americans wrongfully detained in Iran,” said a senior administration official, who was not authorized to speak on the record.

A State Department spokesperson on Tuesday described Zakka as having been "unjustly detained in Iran for almost four years," adding they hoped Zakka’s release was “a positive sign,” for other American detainees in Iran.

“The United States continues to call on the Iranian regime to release missing and wrongfully detained American citizens," the spokesperson said.

Zakka’s lawyer said his client called for the release of other foreign nationals held in Iran. “Nizar also wants to remind those who can help that there remain many Americans, US LPRs (legal permanent residents), and other foreigners in Iranian prisons. Nizar grew close to some of these men; they need help and want to come home,” Poblete said.

With tensions rising between Tehran and the Trump administration, and as U.S. sanctions squeeze the Iranian economy, Zakka’s release could signal a potential opening in the standoff.

The move comes against the backdrop of a flurry of diplomatic activity by U.S. allies aimed at lowering the temperature between the two adversaries. German Foreign Minister Heiko Maas met his Iranian counterpart on Monday in Tehran and Japan’s Prime Minister Shinzo Abe was due to fly to Tehran on Wednesday.

It’s unclear if Zakka’s release could open the door to the release of other foreigners held by Iran, including several Americans.

Although Iran in recent weeks has portrayed Zakka’s case as an issue between Iran and Lebanon, Iranian Foreign Minister Javad Zarif in 2016 said it was a problem primarily between Tehran and Washington. The Trump administration has cited the imprisonment of foreigners as one of a number of practices and policies that Tehran must stop to open the way for negotiations and an end to sanctions.

Zakka ran the Arab ICT Organization, an industry consortium that promotes information technology and internet freedom in Arab countries. Zakka was arrested on the way to the airport by Iran’s Revolutionary Guard and was later sentenced to 10 years in prison on espionage charges in a closed-door trial.

In an interview last year, an adviser to Iranian President Hassan Rouhani, Shahindokht Molaverdi, expressed regret at Zakka’s imprisonment after she invited him to a conference and blamed it on the hard-line judiciary and limited authority of the civilian government.

“This is in no way approved by the government,” Molaverdi told the Associated Press. “We did all we could to stop this from happening, but we are seeing that we have failed to make a significant impact.”

Zakka's family and human rights groups have dismissed the allegations as without any foundation.

At least 11 dual and foreign nationals, or Iranian citizens with foreign residencies, not including Zakka, are imprisoned in Iran as of this month, according to the Center for Human Rights in Iran.

Those imprisoned include Siamak Namazi, an Iranian-American businessman, and his elderly father Baquer Namazi, a former UNICEF official; Xiyue Wang, an American graduate student from Princeton University; Morad Tahbaz, who has U.S., British and Iranian citizenship and was detained along with other environmental activists; and Michael White, a U.S. Navy veteran.

In early May, the U.S. ramped up economic pressure against Iran, threatening sanctions against any country that imports Iranian oil.

Zarif said Monday that the U.S. could not “expect to stay safe,” after launching what he called an economic war against Iran.

"Whoever starts a war with us will not be the one who finishes it," Zarif said at a news conference with Maas.

Iran threatened in late May to quadruple their production of enriched uranium unless Europe found a way to provide economic relief from U.S. sanctions.

One year after the U.S. withdrew from the Iran nuclear deal, Maas traveled to Tehran to try to rescue the accord from failing entirely.

The head of the U.N.’s International Atomic Energy Agency, Yukiya Amano, said Monday that Iran has in recent weeks increased its production of enriched uranium. But he said it was unclear when the country’s stockpile would surpass the set limits of the deal and expressed concern about the increased tension surrounding the issue.

State Department spokesperson Morgan Ortagus said the increased production shows that “Iran is going in the wrong direction, and it underscores the continuing challenge Iran poses to international peace and security.”