A series of air strikes on an opposition-held district in Homs, Syria's third-largest city, have killed at least nine civilians, activists said.
Pro-government forces, presumably Russia or Syria, shelled the city's al-Waer neighbourhood with tank and artillery fire in conjunction with the air strikes, the Local Co-ordination Committees, an activist network, reported.
Government forces have kept the opposition-held neighbourhood under siege since 2013, according to the Washington-based Siege Watch.
An estimated 75,000 people are trapped inside.
The local civil defence search-and-rescue team, also known as the White Helmets, said the air strikes hit one of its centres in al-Waer, wounding one volunteer.
The government and its allies have regularly targeted hospitals and first responder positions in the course of the Syrian civil war, which is approaching its seventh year.
The British-based Syrian Observatory for Human Rights also said nine civilians were killed in the raids.
Government forces retook most of the city in 2014, effectively ending an anti-government protest movement that had gripped Homs since 2011.
The al-Waer assault came a day after presumed Russian or Syrian government aircraft bombed the rebel-held city of Idlib and marked the second major violation of a month-old ceasefire between the government and rebels in as many days.
The Observatory said 24 civilians were killed in seven strikes across Idlib on Tuesday and the Idlib Civil Defence said 26 people were killed.
The December 30 ceasefire was brokered by Russia and Iran, both key allies of Syrian president Bashar Assad, and Turkey, which supports the opposition.
Each side has accused the other of repeated violations.
United Nations-sponsored talks on Syria are due to start in Geneva on February 20 and invitations to the discussions will be issued "in the coming days", UN spokesman Stephane Dujarric said.
He said UN special envoy Staffan de Mistura and his team were continuing discussions and the invitations would go out once they reached "a position of comfort".
Earlier Mr de Mistura said invitations would be issued around Wednesday and if the Syrian opposition was not united, he would select the delegation and ensure it was as inclusive as possible.
Mr Dujarric would not say whether talks with opposition groups were still going on or whether Mr de Mistura was choosing the opposition delegation.
Later, the Pentagon said two US air strikes near Idlib last week killed 11 al Qaida operatives, including one with ties to Osama bin Laden and other senior al Qaida leaders.
Navy captain Jeff Davis said an air strike on Friday killed 10 operatives in a building used as an al Qaida meeting site and a raid the next day killed Abu Hani al-Masri, who US officials say oversaw the creation and operation of al Qaida training camps in Afghanistan in the 1980s and 1990s.
Al-Masri had ties to bin Laden and to Ayman al-Zawahiri, who became the leader of al Qaida when bin Laden was killed by US forces in 2011, Capt Davis said.
Turkey, meanwhile, is in talks with Russia to co-ordinate troop movements around northern Syria to avoid any encounter with the Syrian military, Turkish president Recep Tayyip Erdogan's spokesman said.
Syrian government forces and Turkish-backed opposition fighters are in a race to seize the town of al-Bab from the Islamic State terror group.
Turkish and Syrian forces have so far avoided direct conflict, despite hostile rhetoric between Mr Erdogan and Assad.
The twin offensives put the two forces within two miles of one another, on opposite sides of al-Bab.
Mr Erdogan's spokesman Ibrahim Kalin said Turkish troops had reached the centre of al-Bab and were fighting to secure it, but the Syrian Observatory for Human Rights, which relies on a network of activists inside Syria, said the Turkish force was still on the town's outskirts.