At least 60 Shiite villagers died in clashes with rebels in eastern Syria while twin suicide bombings hit Damascus as the West moved to support the opposition following battlefield losses against pro-regime forces.
Despite Tuesday's attacks, Bashar al-Assad's regime, dominated by his Alawite sect of Shiite Islam, appears to have gained the upper hand against mainly Sunni Muslim rebels, buoyed by military support from its Shiite allies, Hizbollah and Iran.
With regime forces gaining ground, France said the nearly 27-month conflict, which is estimated to have killed at least 94,000 people, is at a "turning point" and that it is time to review whether to arm the opposition.
The issue of military support is likely to top the agenda when US Secretary of State John Kerry meets in Washington with British counterpart William Hague on Wednesday.
"Armed Shiite villagers attacked a nearby rebel post yesterday and killed two. Today (Tuesday) rebels attacked the village and took control of it, killing 60 Shiite residents, most of them fighters," Rami Abdel Rahman, director of the Syrian Observatory for Human Rights, told AFP.
The clashes came in the majority Sunni village of Hatlah, in eastern Deir Ezzor province.
At least 10 rebels were also killed in the fighting on Tuesday, and Shiite residents of Hatlah were fleeing following the violence, Abdul Rahman said.
Earlier in Damascus, two suicide bombings left at least 14 people dead and 31 wounded, and caused widespread damage in the Marjeh neighbourhood, state media and the rights Observatory said.
The Observatory said one of the blasts "was caused by a suicide bomber who blew himself up inside the police station".
Syria's cabinet denounced the attack, saying "armed terrorist groups and those behind them have failed completely because of the victories achieved by our brave army".
Forces loyal to President Assad, including thousands of Lebanese Hizbollah fighters, have overrun rebel fighters in central Syria in the past week, including in the strategic town of Qusayr.
"There are lessons to be drawn from what happened in Qusayr and what is happening in Aleppo," said French foreign ministry spokesman Philippe Lalliot.
"We are at a turning point in the Syrian war. What should we do under these conditions to reinforce the opposition armed forces? We have had these discussions with our partners, with the Americans, the Saudis, the Turks, many others.
"We cannot leave the opposition in the current state."
Plans to bring together members of Assad's regime and the opposition at talks in Geneva have so far failed to come to fruition, and Hague at the weekend warned that regime gains on the ground raised new hurdles.
US President Barack Obama has asked his national security team to "look at all options" to end the fighting, State Department spokeswoman Jen Psaki reiterated Tuesday, adding however there would be no American "boots on the ground".
Damascus has also benefited from political support on the international stage from Russia, which supplies it with weapons and has blocked UN Security Council resolutions condemning it.
But Russian President Vladimir Putin said on Tuesday that he always believed that Assad should have implemented political reforms that could have averted the bloodbath.
In Aleppo province, the army launched multiple attacks on rebel positions, including areas of the Minnigh airbase held by insurgents, the Observatory said.
"Parts of Minnigh military airbase were shelled by regime forces.... Rebels are in control of large swathes of the airbase."
A military source told AFP heavy clashes were raging at the base for a third day, but denied any part of the airport was under rebel control.
Regime forces shelled the opposition-controlled villages of Deir Hafer and Al-Bab, and hit the insurgent stronghold of Marea with rockets, the Observatory said.
The regime has pledged to focus its attention on Aleppo since its triumph in Qusayr, a town on routes to Lebanon and the Alawite coastal heartland that the rebels had held for a year.
Hizbollah's role in that devastating 17-day assault has raised fears about the growing regionalisation of the conflict in Syria, which began in March 2011.
The deteriorating situation on the Golan Heights has prompted Austria to say it will withdraw its troops from the UN monitoring force on the strategic Syrian plateau, most of which is occupied by Israel.
Austria's defence ministry said the withdrawal of its 378 troops would begin on Wednesday.
Violence across Syria killed at least 141 people on Tuesday, 44 of them civilians, according to the Observatory, which relies on a network of activists, medics and lawyers on the ground for its information.