Iran says it is holding the United States responsible for the lives of 48 Iranians kidnapped Saturday in Syria.

State-run media say the Foreign Ministry told the Swiss envoy in Tehran that it expects the U.S. to use its influence to secure their release without any preconditions. Switzerland represents U.S. interests in Iran because Washington and Tehran do not have diplomatic relations.

Iran says the 48 abducted by rebels in Damascus were religious pilgrims, but a brigade commander with the rebel Free Syrian Army described them as elite Revolutionary Guards on a “reconnaissance mission.”

Iranian officials have reached out to Turkey and Qatar for help in securing the hostages’ release.

Iran’s Foreign Minister Ali Akbar Salehi is visiting Turkey Tuesday to discuss the Syrian crisis with counterpart Ahmet Davutoglu. Iranian officials said the issue of the hostages would be discussed.

Syrian rebels say three of the Iranians were killed Monday in attacks by Syrian President Bashar al-Assad’s forces, but that has not been independently confirmed.

Iran backs the Syrian government, while Turkey and Qatar support the Syrian opposition.

Also Tuesday, Iranian state media said the secretary of Iran’s National Security Council, Saeed Jalili, traveled to Damascus for talks with Syrian President Bashar al-Assad and other senior officials.

Government ‘crumbling’

The meetings come amid continued violence in the country’s 17-month uprising and what the U.S. says are signs President Assad is losing his grip on the country.

The Syrian government suffered a significant blow Monday when Prime Minister Riyad Hijab defected, two months after taking the top post.

Hijab said he defected. Syrian state media said he was fired.

“I announce today my defection from the killing and terrorist regime and I announce that I have joined the ranks of the freedom and dignity revolution,” Hijab said in a statement read in his name on Al-Jazeera television.

U.S. officials say the defection shows President Assad’s government is “crumbling.”

“As we’ve said repeatedly as we’ve seen more and more high-level defections, this is a sign that Assad’s grip on power is loosening,” said White House spokesman Jay Carney. “If he cannot maintain cohesion within his own inner circle, it reflects on his inability to maintain any following among the Syrian people that isn’t brought about at the point of a gun.”

“It’s clear that these defections are reaching the highest levels of the Syrian government, and Assad cannot restore his control over the country because the Syrian people will not allow it,” Carney said. “The quickest way to end the bloodshed and suffering of the Syrian people is for Assad to step aside to enable a peaceful political transition to a government that is responsive to the aspirations of the Syrian people.”

Jordanian officials said Hijab defected to Jordan with his family. But Syrian state media said he had been “relieved of his duties” and that his deputy, Omar Ghalawanji, was replacing him in a “caretaker” capacity.

A spokesman, Mohammed Otri, told journalists that Hijab had been planning his defection for a long time. He said the defection did not occur on the spur of the moment, but that it had been planned for several months in coordination with the rebel Free Syrian Army.

Violence continues

Meanwhile, Syrian opposition activists say government forces were shelling neighborhoods in the nation’s largest city of Aleppo Tuesday. The Syrian Observatory for Human Rights said clashes were taking place between rebels and Assad’s forces in several areas of the city, while in all of Aleppo province, it said 12 civilians had been killed.

The Observatory also reported deadly shelling in Homs and Idlib provinces and explosions in Reef Dimashq province, as well as fighting in the city of Deir Ezzor.

The group says more than 270 Syrians were killed in violence across the country on Monday, with 186 of them civilians. In all, the activists say more than 20,000 people have been killed since the uprising began in March of last year.

Government and opposition claims in Syria are difficult to verify because journalists do not have freedom of movement.