Renewed battles between Syrian government forces and rebel fighters rocked Damascus on Saturday, and clashes were reported in at least half a dozen other cities across the country.

The Syrian army hammered an area of the capital with artillery, mortar fire and helicopter rockets as rebels and soldiers battled near the presidential palace. Heavy fighting also continued unabated in the northern city of Aleppo, the country’s largest, which has become the scene of a raging urban war after remaining relatively quiet for much of Syria’s nearly 17-month-old uprising.

The violence Saturday left at least 145 people dead across the country, according to the Local Coordination Committees, an activist network. Syrian President Bashar al-Assad, however, stayed out of public view, as he has done since a bombing in Damascus on July 18 that killed four top security officials.

Amid the turmoil, gunmen kidnapped 48 Iranian pilgrims from a tour group bus in Damascus. The group was on its way to a Muslim shrine popular with Shiites shortly before noon when the bus was attacked, according to an Iranian Embassy official in Damascus quoted by Iran’s semiofficial Fars News Agency.

A week ago, Syrian Foreign Minister Walid al-Moualem had proclaimed the defeat of rebel forces in Damascus and predicted they would soon be defeated in Aleppo, as well. But the renewed fighting in the capital, as well as the mass kidnapping, signaled the possibility that Syrian security forces are losing their grip on the city.

The Iranian Embassy official noted that Iran’s government has halted official tours to Syria, presumably because of the widespread violence, and that the pilgrims kidnapped Saturday had arranged a private tour.

A photo of the bus published by Fars News showed a cracked windshield with at least one bullet hole, suggesting that the gunmen had fired on the vehicle to force the driver to stop.

Iranians have been kidnapped before in Syria. Since the country’s uprising started in March 2011, 32 Iranians, including seven engineers, 22 pilgrims and three truck drivers, have been kidnapped there, according to the official Islamic Republic News Agency (IRNA). Although 27 of them have been released, five — two engineers and the three drivers — are being held by armed groups.

None of the armed opposition groups in Syria had asserted responsibility for the kidnapping by late Saturday, but a Syrian government official quoted by Fars News blamed “terrorists linked to the Free Syrian Army.” Col. Malik Kurdi, the deputy commander of the Free Syrian Army, said when reached by phone that he had no information about the identity of the perpetrators.

An Iranian Embassy official quoted by IRNA said that the pilgrims had been located and that the embassy was following up with Syrian officials to secure their release.

The kidnapping could represent an attempt by opposition groups to pressure the Iranian government, which is Assad’s strongest regional ally, to withdraw its support for or denounce the Syrian government, analysts say.

A Syrian opposition group that kidnapped 11 Lebanese pilgrims in late May demanded that Hezbollah leader Hasan Nasrallah, who is also one of Assad’s staunchest supporters, apologize for comments in support of the Syrian leader as a precondition for releasing the captives.

Meanwhile, a relatively unknown Islamist opposition group called the al-Nusra Front asserted in a statement posted online Friday that it had kidnapped Mohammed al-Saeed, a Syrian TV presenter, on July 19 and subsequently killed him, according to the SITE Intelligence Group. “Perhaps this operation and others will serve as an example to all who support this tyrannical regime, so that they may repent to Allah,” the statement said, according to the SITE translation.

The Islamist group also said it had raided a police station in the Jdeidat Artouz suburb of Damascus, and it posted pictures of assault rifles, pistols and ammunition that it said had been taken from the station.

The Syrian army deployed artillery, mortar fire and helicopter rockets against the Tadamon neighborhood in Damascus, as rebels and soldiers fought fiercely in Muhajereen, near the presidential palace, Saturday evening, according to the Local Coordination Committees. The eastern city of Deir al-Zour was also heavily shelled, the group said.

In Aleppo, the army battered the neighborhoods of Salahuddin and Hanano with artillery fire Saturday as jets attacked the nearby village of Marasta, according to the Britain-based Syrian Observatory for Human Rights, an opposition group. Clashes also erupted between rebel fighters and government troops around the ancient citadel in the center of Aleppo, the observatory group said.

The dead Saturday included 21 people in Deir al-Zour, 53 in Damascus and its suburbs and 21 in Aleppo, according to the Local Coordination Committees.

The escalation in fighting comes as the beleaguered Syrian government shows signs that international sanctions may be starting to hit hard. On Friday, Deputy Prime Minister Qadri Jamil said the government had requested a loan from Russia.

Suzan Haidamous contributed to this report.