Syrian warplanes have carried out several air raids on rebel-held areas in and around Damascus, while fresh clashes between troops and rebels have erupted in the eastern and southern suburbs of the capital, according to an activist group.
The government also used fighter jets to bombard the rebel-held towns of Yabroud, Douma and Harasta, east of Damascus, as well as Sbeineh, southwest of the capital, the Syrian Observatory for Human Rights (SOHR) said on Monday.
"At least one civilian was killed in an air strike on Qaboon" in northeast Damascus, SOHR said, "while regime troops pounded the district of Jobar" in the east.
Meanwhile, "fierce clashes raged on the edges of Jobar [in eastern Damascus], near Abbasiyeen Square", according to SOHR, which relies on a broad network of activists, doctors and lawyers for its reports.
In-depth coverage of escalating violence across Syria
Rebels view the square as a strategic target because it lies well within the confines of Damascus, President Bashar al-Assad government's main bastion of power.
SOHR also reported the army's use of heavy artillery fire on Yarmuk in southern Damascus, with tanks also striking other rebel enclaves nearby.
Elsewhere in Syria, jet fighters hit targets in the northeastern city of Raqqa as well as an area near the government-held Base 17 in the eponymous province.
Raqqa's provincial capital fell into rebel hands in early March, and fighters have since been fighting to gain control of Base 17, one of the army's few remaining bastions in the province.
In coastal Syria, "the army launched a massive operation ... in the north of Latakia province", near the Turkish border, attacking rebel-held villages, the pro-government Al-Watan newspaper said.
According to a preliminary toll for Monday, at least 22 people were killed in violence across Syria, SOHR said.
Muslim Brotherhood denial
In a separate development, the exiled leader of Syria's Muslim Brotherhood denied on Monday widespread accusations by other pro-rebel political factions that the group was seeking to impose its will on other members of the country's opposition.
The rare news conference by Mohammad Raid al-Shaqfa highlights the suspicions that his movement has raised in an already fractured opposition.
The Islamist group has a powerful donor network among members in exile and supporters in oil-rich Gulf countries. Many in the opposition say the Brotherhood uses its support and money as key levers for influence.
"Our aim is not to tear apart but to unite the [Syrian] opposition," Shaqfa said in the Turkish city of Istanbul, where he is based.
He blamed accusations against his group on "lies and fabrications" that he said were spread by the Assad regime.
In yet another development on Monday, a Syria-based human rights group said in a report that Assad's military unit in charge of protecting Damascus was running secret prisons holding hundreds of suspected regime opponents.
The Violations Documentation Centre said the regime army's Fourth Division was running detention centres in its bases in and around Damascus.
The division is commanded by Maher Assad, the president's younger brother. It is considered a pillar of military forces and is charged with defending the capital, the seat of Assad's power.
The centre, which has tracked the dead, wounded and missing since the start of the uprising in March 2011, said it interviewed former detainees, who had been held in small crowded cells and beaten by guards.
Bashar El-Ahmed, a 31-year-old schoolteacher, said he was taken blindfolded to the detention centre and realised after arrival that he was underground.
He said guards beat him with batons, electric prods and cables. The report said El Ahmed was accused of human right activism.
The claims could not be independently verified, but other rights groups, including the US-based Human Rights Watch, have said thousands of opposition members, protesters and their families have been detained since the revolt against Assad's rule started in March 2011.