The Free Syrian Army has sacked its leader after the Western-backed rebels suffered repeated setbacks, amid signs of an escalation in fighting that has already killed more than 140,000 people.
Activists warned Monday that regime troops are preparing a ground offensive against Yabrud, the last rebel-held stronghold in the strategic Qalamun region near the border with Lebanon, after days of aerial bombardment.
On the diplomatic front, US Secretary of State John Kerry slammed Russia on Monday for "enabling" Syria's President Bashar al-Assad to stay in power, after Geneva peace talks broke off Saturday without any result.
Moscow dismissed the allegation and accused the United States of failing to ensure that a "truly representative opposition delegation" attended the talks.
The sacking of rebel military commander Selim Idriss was announced Sunday by the FSA, which said he was being replaced by Brigadier General Abdelilah al-Bashir, another army deserter.
Colonel Qassem Saadeddine of the rebel coalition said the decision was taken because of "the paralysis within the military command these past months" and the need to "restructure."
But Aron Lund, editor of the Carnegie Endowment's Syria in Crisis website, said he suspected there was more to the decision.
"It appears that Idriss may have been blocking a Saudi-backed plan to revamp" the FSA's Supreme Military Council, said Lund.
Saudi Arabia has been a leading provider of military support to the Sunni-led rebels in a bid to counter the regional influence of Shiite Iran, a key ally of the Assad regime.
The FSA has taken a beating in recent months not only from regime forces but also from Islamist fighters who have joined the battle to unseat Assad.
Considered the "moderate" rebel group, the FSA was once Syria's strongest armed opposition force but is now increasingly marginalised by Islamists, including Al-Qaeda-inspired groups.
- Local truce in effect -
The official SANA news agency said the army on Monday recaptured an Alawite village in central Hama province where rebels "massacred" civilians earlier this month.
In the Damascus area, meanwhile, a local truce went into effect in the southern suburb of Babbila, the latest in a series of local ceasefires in flashpoints around the capital.
An AFP reporter who visited the area under official escort said talks are taking place to arrange similar agreements in other areas.
But analysts said that with the failure of the latest round of peace talks, the regime and rebels are likely to ratchet up military operations.
"It will probably get worse before it gets better," said Volker Perthes, director of the German Institute for International and Security Affairs.
"Both sides will try to show that they can change the balance on the ground in their favour, and that they aren't forced to negotiate out of weakness."
The Syrian Observatory for Human Rights, a Britain-based monitoring group, reported a surge of fighting Monday around Yabrud, on a strategic highway linking Damascus and the central city of Homs.
The head of the Observatory, Rami Abdel Rahman, told AFP Syrian warplanes dropped explosive-packed barrels on the town's outskirts, and that fighting had erupted in the nearby rebel-held towns of Ras al-Maara and Al-Sahel.
Pro-regime newspaper Al-Watan reported that troops were battling jihadists around Yabrud, including fighters from Al-Nusra Front, Al-Qaeda's branch in Syria.
Fighters from the Lebanese Shiite movement Hezbollah are helping regime forces in the Yabrud offensive, and Hezbollah leader Hassan Nasrallah on Sunday said it was only "a question of time" before the rebels are defeated.
The Observatory meanwhile updated the toll of a Friday car bombing in the southern Daraa province to 49, including four children.
- Diplomatic efforts stumble -
The flare-up comes as diplomatic efforts to try to end the conflict seem to have ground to a halt.
US Secretary of State John Kerry said in Jakarta that the Damascus regime "stonewalled" in Geneva with "increased support from Iran, from Hezbollah and from Russia."
"Russia needs to be a part of the solution and not be distributing so much more weapons and so much more aid that they're in fact enabling Assad to double-down."
Russian Foreign Minister Sergei Lavrov hit back, telling reporters in Moscow that the opposition delegation in Geneva did not include some of the most important members of the National Coalition umbrella group.
"They (Washington) assured us that they will be doing everything possible to ensure there is a truly representative opposition delegation," Lavrov said.
"For now, they have been having trouble doing this."