BEIRUT — Syria’s former prime minister, who fled the country last week, said Tuesday in his first public appearance since his defection that the government of President Bashar Assad was crumbling internally under the pressure of relentless fighting against rebels and from betrayals by loyalists who want only to flee.

‘‘Based on my experience and my position, the regime is falling apart morally, materially, economically,’’ the former official, Riad Farid Hijab, said at a news conference in Amman, Jordan. ‘‘Its military is rusting, and it only controls 30 percent of Syria’s territory.’’

He said that many high-level civilian and military officials in Syria — ‘‘leaders with dignity’’ — were waiting to defect. Hijab said he fled the Syrian capital, Damascus, because the government had threatened his family and had no reasonable means to end the violence. He also urged the opposition to unify and move ahead with plans for a transitional government and ‘‘a civilian democratic state that preserves the right, justice, and dignity of all Syrians.’’

But he said he had no interest in a formal position with a post-Assad government, should there be one.

‘‘I have sacrificed myself in the campaign of righteousness,’’ he said. ‘‘I don’t want to satisfy anyone but God.’’

Hijab’s repudiation of the Assad government was welcomed in the United States, where the Treasury Department removed his name from a blacklist of high Syrian officials whose assets have been frozen by US sanctions. In a statement announcing Hijab’s removal from the blacklist, the Treasury Department said it hoped that other Syrian officials would take ‘‘similarly courageous steps to reject the Assad regime and stand with the Syrian people.’’

Hijab’s claims about the weakness of the Assad government could not be independently verified, and he gave few details to support his assessment. Hijab, a Sunni technocrat from the eastern city of Deir el-Zour — which has been enduring shelling and fighting for weeks — was not a member of Assad’s inner circle, and he was appointed to the position of prime minister only in June.

But analysts have said that as the highest-level civilian official to defect, he may have had access to reliable internal assessments or government sources.

His argument that the government is weakening follows similar descriptions from other defectors, who have suggested that Assad’s grip on power has been loosening even as Syria increasingly becomes the arena for a proxy war, with Iran and Russia assisting the government as Turkey, Qatar, and Saudi Arabia funnel military aid to the rebels, supplemented with nonlethal assistance from the United States.

The Obama administration has resisted an intensified clamor by Syrian insurgents for military help from the United States, including ammunition and the imposition of a no-fly zone in Syria to deter the Syrian air force from bombing rebel targets.

While the administration has not ruled out any option on Syria, US officials have repeatedly said they do not want to further militarize the conflict. Defense Secretary Leon E. Panetta reiterated that view in an interview Monday with the Associated Press, asserting that plans for a no-fly zone in Syria were ‘‘not on the front burner as far as I know.’’

On Tuesday, the rebels said the fight for control continued. In Aleppo, Syria’s largest city, where communications seemed to be limited, fighting continued Tuesday, with rebels trying to hold contested areas amid an extended government ground assault.

In and around Damascus, activists reported heavy shelling and growing numbers of refugees flowing out of the city.

Inside the city, heavy clashes were reported in the neighborhood of Tadamon, a rebel-controlled area that abuts Yarmouk, Syria’s largest Palestinian neighborhood, and in an area called Qabbon, where sectarian fighting between Alawites and Sunnis appeared to have caused a mass exodus.