President Bashar Al Assad's forces have overrun the rebel bastion of Idlib in northwest Syria, activists said Wednesday.
The opposition also suffered a setback on the political front with resignations from the Syrian National Council (SNC), an umbrella movement of anti-regime groups.
"Since last night there has been no more fighting," said Noureddin Al Abdo, an activist in Idlib, confirming earlier reports by a government newspaper that the city had fallen after a four-day assault by regime forces.
"The (rebel) Free Syrian Army (FSA) has withdrawn and regime forces have stormed the entire city and are carrying out house-to-house searches," said Abdo, reached by telephone from Beirut.
The army launched its assault on the rebellious province of Idlib near the Turkish border on Saturday, bombarding the city of the same name and outlying regions in a bid to root out armed insurgents.
"The FSA preferred to withdraw because everyone knows it cannot resist the army," Abdo said.
The Syrian Observatory for Human Rights said fierce clashes between regime forces and rebel troops were ongoing in the Jabal Al Zawiya district of the province and at least four people had died on Wednesday.
"Seventeen soldiers were killed late Tuesday after armed rebels attacked checkpoints in the village of Al-Barra, in Jabal Al Zawiya," said the Britain-based group.
The capture of Idlib comes two weeks after regime forces stormed the Baba Amr rebel stronghold in the central city of Homs following a month-long blitz that left hundreds dead. It also comes as Assad's regime responded to UN-Arab League proposals to end a 12-month crisis that has killed more than 8,500 people, mostly civilians, according to activists.
A spokesman for UN-Arab League envoy Kofi Annan, who met with Assad in Damascus over the weekend and made "concrete" proposals to halt the bloodshed, said the unspecified Syrian response was being considered.
Russia insisted on Wednesday that it was defending "fairness" rather than its allies in the regime in Damascus.
"We are not defending the regime but fairness, the sovereign right of the Syrian people themselves to have a democratic choice," Interfax quoted Foreign Minister Sergei Lavrov as telling a parliamentary hearing.
Foreign intervention or outright support for the rebels could lead to a "ruinous civil war with unpredictable regional consequences," Lavrov stressed.
Russia on Tuesday said it would press Assad to accept foreign monitors who could observe the implementation of a simultaneous ceasefire between government troops and rebels.
The opposition, which is heavily outgunned by the regime and has called for its fighters to be armed in the defence of civilians, was hit on Wednesday by resignations from SNC ranks.
Haitham Al Maleh, Kamal Al Labwani and Catherine Al Talli announced on their Facebook pages were they quitting due to "differences" and the "inefficiency" of the SNC, an opposition coalition of Islamists, liberals and nationalists.
Amnesty International warned on Wednesday of the "nightmarish world of systematic torture" faced by detainees in Syria.
"The scale of torture and other ill-treatment in Syria has risen to a level not witnessed for years," Amnesty said in a report based on testimony from survivors who fled to Jordan.
The UN human rights office is to send observers to Syria's neighbouring countries to collect evidence and document atrocities, the deputy rights commissioner said.
"We will be sending monitors for information collection and documentation of the violations and atrocities in the border areas in the neighbouring countries later this week," said Kang Kyung-wha.
Assad on Tuesday issued a decree setting May 7 as the date for parliamentary elections under a new constitution adopted in February. But Washington immediately dismissed the planned vote as "ridiculous." "Parliamentary elections for a rubber-stamp parliament in the middle of the kind of violence that we're seeing across the country -- it's ridiculous," US State Department spokeswoman Victoria Nuland said.