Syria's former prime minister, Riyad Hijab, has claimed Bashar al-Asssad's regime is on the point of collapse, having lost control of two-thirds of the country, as he called on other top officials to follow his example and defect.

In his first public appearance since he fled Damascus with his family a week ago, Hijab told a press conference in the Jordanian capital, Amman, the Syrian army needed to "take the side of the people".

"I assure you, from my experience and former position, that the regime is collapsing, spiritually and financially, as it escalates militarily," Hijab said. "It no longer controls more than 30% of Syrian territory."

Hijab said that while he was prime minister he had been unable to stop the regime's policy of using heavy artillery against Syrian cities considered by the regime as being opposition strongholds. He said he had felt "pain in my soul" of the shelling of civilian areas.

"I was powerless to stop the injustice," he said, urging other senior figures to defect. "Syria is full of honourable officials and military leaders who are waiting for the chance to join the revolution. I urge the army to follow the example of Egypt's and Tunisia's armies take the side of people."

Opposition figures claim many other leading military and political figures in the regime have swapped sides but remained at their posts, either out of fear of what would happen to their families if they defected, or because they had been asked to stay by the rebels to supply intelligence on the inner workings of Assad's government.

Hijab is the highest-ranking defector to date. His flight from Damascus came a month after the defection of a Republican Guard general and former member of Assad's inner circle, Manaf Tlass, and the Syrian ambassador to Baghdad, Nawaf al-Fares.

In the past week the head of protocol at the presidential palace, Muhi al-Din Maslaman, has also defected.