A car bombing in Damascus on Sunday killed at least nine security forces, a watchdog said, as aid groups urged the evacuation of civilians trapped in the embattled Syrian town of Qusayr.
The Syrian Observatory for Human Rights said the explosion, in the east of the capital, appeared to have been carried out by the extremist Al-Nusra Front, which is allied with Al-Qaeda, although there was no immediate confirmation.
In Lebanon, security sources said two rockets fired from Syria landed in a border area, and Israeli war planes could be heard flying low over several parts of the country.
"At least nine regime forces were killed in the explosion of a car bomb near a police station in the Jubar neighbourhood," Observatory director Rami Abdel Rahman told AFP.
Syrian state news agency SANA reported "preliminary information on a car bomb explosion in Jubar," but gave no further details.
The Observatory said fierce clashes between rebels and regime forces were ongoing in Jubar, a contested neighbourhood which has been targeted by regime air strikes and mortar attacks for several months.
Elsewhere in the capital, the Observatory said, regime forces shelled the Al-Hajar Al-Aswad, Assali and Qaddam neighbourhoods in the south and southwest of the city overnight.
The attack came as international aid groups called for the evacuation of civilians trapped in the flashpoint central Syrian town of Qusayr.
Regime forces launched an assault against the rebel stronghold two weeks ago, and concern has risen over the fate of thousands of civilians, including around 1,500 wounded residents.
Abdel Rahman told AFP on Saturday that "the opposition fighters are fighting with everything they've got.
"Regime forces are reinforcing the sites that they have north of the city," he said.
The group said at least 15 tanks were massed north of Qusayr, a prize for both the regime and the rebels as it links Damascus to the coast, and is near the Lebanese border, providing a key rebel conduit for weapons and fighters.
Abdel Rahman said around 1,000 wounded people were trapped inside Qusayr but UN officials suggested the figure could be even higher.
"We understand there may also be as many as 1,500 wounded people in urgent need of immediate evacuation for emergency medical treatment, and that the general situation in Al-Qusayr is desperate," said a joint statement by UN humanitarian chief Valerie Amos and UN human rights commissioner Navi Pillay.
They were "extremely alarmed" by reports that civilian neighbourhoods were under fire, they added.
"We urge the parties to agree to an immediate ceasefire to allow humanitarian agencies to evacuate the wounded and provide life-saving treatment and supplies."
In New York, UN chief Ban Ki-moon urged "all sides to do their utmost to avoid civilian casualties," spokesman Martin Nesirky said in a statement.
Ban also called on all sides to help trapped civilians escape the town.
In Geneva, the International Committee of the Red Cross (ICRC) also expressed alarm.
"Civilians and the wounded are at risk of paying an even heavier price as the fighting continues," said Robert Mardini, head of Middle East operations.
He called for restraint on all side, adding that the ICRC had already requested access to the town.
The fighting in Syria has increasingly drawn in neighbouring Lebanon, despite Beirut's official neutrality on the conflict.
Members of the powerful Lebanese Shiite group Hezbollah, a staunch ally of President Bashar al-Assad's regime, are fighting alongside government troops.
And some members of Lebanon's Sunni Muslim community have also crossed the border to fight alongside the Sunni-led rebels, encouraged by clerics including the influential Qatar-based Yusuf al-Qaradawi.
On Sunday, Lebanese sources reported the death of a Hezbollah fighters near Zabadani, northwest of Damascus.
And the Observatory and family members said a Sunni Lebanese member of the Al-Nusra Front was killed fighting Hezbollah members in the Qusayr area.
The fighting spilled over again, with two rockets fired from Syria landing in the northeastern Hermel region, a Hezbollah stronghold.
And AFP correspondents across Lebanon reported unusually loud and low Israeli war plane overflights in several parts of the country, including Beirut.