Reports that a top official in the government of Moammar Gaddafi has defected gained strength here Tuesday, as a spokesman for the Libyan government said the regime has been unable to make contact with the man.

Shokri Ghanem, Libya’s top oil official, left Libya on Monday to go to Tunisia on “official business,” said Moussa Ibrahim, spokesman for the Libyan government. Ibrahim told The Washington Post that Libya had not been able to reach Ghanem since Monday night.

But a Tunisian official said Tuesday that Ghanem — described in leaked State Department cables as, at one time, one of the few people in Libya who could openly challenge Gaddafi — had traveled to Tunisia for personal, not official, reasons.

Neji Zairi, a spokesman for the Tunisian Interior Ministry, said Ghanem had entered Tunisia on Saturday with his family on a personal visit, according to registration information at the Ras Jdir border control post. Zairi said that Ghanem had left the Tunisian resort area of Djerba on Tuesday morning but that he did not know his precise whereabouts.

“He’s still in Tunisia,” Zairi said. “I don’t know what he’s doing.”

Ghanem’s defection, if confirmed, would be the highest-profile departure from Gaddafi’s embattled government since Musa Kusa, the foreign minister, sought safe haven in London at the end of March. Coming after three months of armed revolt and as NATO warplanes continue to pound Gaddafi’s home-and-office complex, a defection could be seen as evidence of strains at the very top of Gaddafi’s regime.

Despite the efforts of the ragtag rebel army, the Libyan opposition is unlikely to take Tripoli by force. Instead, analysts say, if Gaddafi goes, it will more likely stem from such diminished support inside his government, from the NATO bombardment that has been targeting Tripoli in recent days, or from a combination of the two.

Ibrahim played down the potential impact of Ghanem’s defection. “It’s not a big deal for us” if he did defect, Ibrahim said, repeating the mantra that the Libyan government is far greater than any one individual. “If he did, this is his business.”

Ghanem is the head of the National Oil Corp., the top oil official in the oil-rich country. He previously served three years as prime minister, leaving that post in 2006. Classified State Department cables made public by WikiLeaks say that he has a PhD from the Fletcher School at Tufts University.

“Ghanem is a comparatively well-respected technocrat who enjoys a reputation as one of the only senior [Libyan government] officials who can speak candidly, and at times openly contradict, Muammar al-Qadhafi,” according to a State Department cable from 2008. But the cable spoke of Ghanem’s frustrations with the Libyan government, even before the current conflict.

In Ghanem’s opinion, according to the cable, “meaningful economic and political reform will not occur while al-Qadhafi is alive.”

Abdel Moneim al-Houni, a former Libyan Arab League representative who was among the first wave of Libyan diplomats to defect, told the Associated Press that Ghanem indeed had defected.

Houni said that he had spoken to Ghanem after he crossed the border but that no official announcement had been made out of concern for the safety of some of Ghanem’s family members who are still in Tripoli, the AP reported.

“Most of the officials remaining in Tripoli are forced to stay under intimidation and pressure. They are not happy with what is happening,” Houni told the AP.

Since Kusa defected, he has been providing information to Western countries, according to Noman Benotman, an analyst at Quilliam, a London counter-extremism think tank who has been in contact with the former Libyan diplomat.

Others who have defected include Interior Minister Abdul Fattah Younis; Justice Minister Mustafa Abdel Jalil; and Ali Abdel Salam al-Treki, a former U.N. General Assembly president. A number of ambassadors and other diplomats also have resigned their posts.

NATO has increased its bombardment of Tripoli in the past week, and economic sanctions have created gas lines and shortages throughout the government-controlled parts of the country.

Also Tuesday, Ibrahim said several foreign journalists who have been detained by Libyan authorities for weeks had been put on trial and were likely to be released within the next day.

Ibrahim identified the journalists as James Foley and Clare Morgana Gillis, American freelance journalists; Manu Brabo, a Spanish freelance photographer; and Anton Hammerl, a South African freelance photographer.

As recently as Monday evening, however, Ibrahim had denied that Hammerl was in Libyan custody and said authorities had no knowledge of his whereabouts. The discrepancy was not explained, and families and editors close to the detained journalists remained skeptical that Hammerl was indeed in custody.

Journalists requested but were not granted permission to see the detainees.