BEIRUT, Lebanon — Syria’s prime minister has fled the country, activists and Syria’s official media reported Monday, in what appeared to be the highest level defection from President Bashar al-Assad’s government thus far.


Jubilant opposition figures said the official, Riyad Farid Hijab, had defected to neighboring Jordan along with at least two ministers and three military officers — 10 families in all, opposition leaders said. Al Jazeera television carried what it said was a statement from a spokesman for Mr. Hijab saying he had “joined the ranks of the freedom and dignity revolution.”


“We welcome the defection,” said Mohammed Sarmini, a spokesman for the Syrian National Council, the main opposition group, based in Turkey. “It’s not the only one and there will be more. This is proof that the regime is collapsing.”


Syria’s state-run news media tried to pre-empt the announcement by saying that Mr. Hijab had been fired as prime minister, a post he had held for less than two months. State news media also disputed news reports that the finance minister had joined the opposition, with the SANA news agency quoting the minister on Monday as calling such reports “untrue.” Opposition activists did not immediately identify the other officials said to have defected.


Mr. Hijab appeared to be the highest ranking civilian official to defect since the conflict started 17 months ago. His departure was the latest signal of disarray among loyalists following a series of high-level defections and a rebel bomb attack last month that killed four top security aides. The Syrian announcement of his dismissal came hours after a bomb explosion was reported at the main state television building in Damascus, the capital. In Aleppo, rebels and reporters in the city, Syria’s largest, said that Syrian jets were dropping bombs. Fierce fighting was reported in other parts of the country.


Iran’s role in the conflict is also growing more tangled. Syrian rebels who captured 48 Iranians near Damascus over the weekend said three had been killed in government shelling and threatened to kill the rest if the shelling did not stop. Earlier the Iranian government called for a broad, international emergency meeting on Syria in Tehran on Thursday.


The rebels holding the captives — from the Bara’a Brigade, one of the myriad groups fighting under the banner of the Free Syrian Army — say the Iranians are members of Iran’s elite Revolutionary Guards. Iran says they are pilgrims who had been visiting an important Shiite shrine near the neighborhood of Tadamon, where fighting has raged for weeks.


Iran’s call for an international meeting came in the diplomatic vacuum created by the international deadlock over the crisis and the failure of peace efforts led by Kofi Annan, the United Nations and Arab League special envoy who last week said he would not renew his mandate at the end of August. Iran’s deputy foreign minister, Hossein Amir Abdollahian, said that 10 countries that all have a “realistic position” on Syria would be participating in an emergency meeting at the ministerial level, scheduled for Thursday.


“The Islamic Republic of Iran believes that a total halt to the violence, and national dialogue, are the solution to control the crisis in Syria, and to that end Iran is organizing this meeting," the state Islamic Republic News Agency quoted Mr. Abdollahian as saying.


Iran, a staunch ally of President Assad, has not been invited to international meetings on Syria. Iran’s foreign minister, Ali Akbar Salehi, has promoted the idea of presidential elections for 2014 and accused “regional countries” of supporting the Syrian rebels.


The departure of Mr. Hijab, a Sunni, cost the Assad government yet another piece of its claim to broad legitimacy. To reinforce loyalty, the Assad family has long stocked the Syrian government with members of its Alawite minority, but to placate other, larger groups, routinely placed non-Alawites in positions of limited authority. According to news reports, Mr. Hijab’s home area is the eastern town of Deir al-Zour, the scene of some intense fighting in recent months.