ALEPPO: While giving no indication that the Obama administration is contemplating military intervention, Mr Panetta said it is increasingly clear that the Syrian crisis is deepening and that Assad is hastening his own demise.

“If they continue this kind of tragic attack on their own people … I think it ultimately will be a nail in Assad’s coffin,” Mr Panetta told reporters travelling with him from Washington. “His regime is coming to an end.”

Mr Panetta said he would use his meetings in Tunisia, Egypt, Israel and Jordan to reinforce an international consensus that Assad must step down and allow a peaceful transition to a democratic form of government.

He said he also will continue consultations on efforts to ensure that Syria’s stockpiles of chemical weapons do not fall into the wrong hands.

Mr Panetta will be in Israel just days after US. Republican presidential hopeful Mitt Romney, who has cast the Obama administration as too soft on Iran and insufficiently supportive of the Jewish state.

In a speech in Jerusalem Sunday, Mr Romney said the United States has “a solemn duty and a moral imperative” to block Iran from achieving nuclear weapons capability. He steered clear of overt criticism of President Barack Obama, even though he said the threat of a nuclear-armed Iran “has only become worse” in the past five years.

Mr Panetta declined to respond. “I’m just not going to get into that game of commenting on what candidates do,” he said.

Mr Panetta said he believes Israeli leaders still support an international campaign of economic, political and diplomatic pressure on Iran to prevent Tehran from obtaining a nuclear weapon.

“My view is that they have not made any decisions with regards to” attacking Iran, he said.

While in Israel, Panetta planned to visit an air defence battery that uses technology developed in part with U.S. support to shoot down short-range rockets. Israel has suffered thousands of rocket attacks from Hizbollah militants in Lebanon and Hamas forces in the Gaza Strip in recent years.

The air defence system, called Iron Dome, has been an important success and serves to deter attacks from Iranian proxies, Panetta said.

He called Iron Dome an example of expanded US-Israeli co-operation.

“We have achieved a level of defence co-operation that is unprecedented in our history,” Panetta said. “And my goal is to deepen that relationship even further.”

This is Panetta’s first visit to Tunis as defense secretary. The country was the launch pad for the wave of revolt that swept through the Arab world in 2011. It had been one of the most repressive governments in the region, while maintaining friendly relations with Washington.

Tunisia’s uprising began in December 2010 when a fruit vendor, Mohammed Bouazizi, set himself on fire in the town of Sidi Bouzid to protest his lack of economic opportunity and the disrespect of the police.

Tunisia’s new government is led by the moderate Islamist Ennahda Party, which had been banned under the previous government. (Agencies)