Rebels thrust into a strategic town in Syria's central Hama province today, activists said, pursuing a string of territorial gains to help cut army supply lines and cement a foothold in the capital Damascus to the south.
They have made a series of advances across the country, seizing several military installations and more heavy weaponry, hardening the threat to President Bashar al-Assad's power base in Damascus 21 months into an uprising against his rule.
Rebels said a day earlier they had captured at least six towns in Hama province. Today heavy fighting erupted in Morek, a town on the highway that runs from Damascus north to Aleppo, Syria's largest city and another battleground.
The opposition-linked Syrian Observatory for Human Rights said rebels were trying to take checkpoints in Morek, one of which they had already seized, and described the town as a critical position for the Syrian army.
"The town of Morek lies on the Damascus-Aleppo road ... it has eight checkpoints and two security and military headquarters. If the rebels were able to control the town they would completely sever the supply lines between Hama and Damascus to Idlib province," the group said in an email.
Idlib is in the rebel-dominated north bordering on Turkey.
The British-based Observatory has a network of activists across the country. Activist reports are difficult to verify, as the government restricts media access into Syria.
Fighting in Hama could aggravate Syria's sectarian strife as it is home to many rural minority communities of Alawites and Christians. Minorities, and particularly the Alawite sect to which Dr Assad himself belongs, have largely backed the president.
Syria's Sunni Muslim majority has been the engine of the revolt.
"Rebels are trying to take Mohardeh and al-Suqaylabiya, which are strongholds of the regime and are strategic. The residents are Christian and the neighbouring towns are Alawite. The rebels worry security forces may be arming people there," said activist Safi al-Hamawi, speaking on Skype.
He said the opposition feared skirmishes that had previously been largely Sunni-Alawite could spread into a broader sectarian conflict.
"I think it is still unlikely, because the residents have tried to maintain neutrality, but if the battle became a sectarian clash, it could be a catastrophe. Christians and Muslims could suddenly find themselves enemies."
UN human rights investigators said Syria's conflict was becoming more "overtly sectarian", with more civilians seeking to arm themselves and foreign fighters - mostly Sunnis - flocking in from 29 countries.
"They come from all over, Europe and America, and especially the neighbouring countries," said Karen Abuzayd, one of UN investigators, told a news conference in Brussels.
The deepened sectarian divisions may diminish prospects for post-conflict reconciliation even if Dr Assad is ousted, and the influx of foreigners raises the risk of fighting spilling into neighbouring countries riven by similar communal fault lines.
President Vladimir Putin of Russia, Assad's main ally and arms supplier, warned that any solution to the conflict must ensure government and rebel forces do not merely swap roles and fight on forever. It appeared to be his first direct comment on the possibility of a post-Assad Syria.
The West and some Arab states accuse Russia of shielding Assad after Moscow blocked three UN Security Council resolutions intended to increase pressure on Damascus to end the violence, which has killed more than 40,000 people. Putin said the Syrian people would ultimately decide their own fate.
Dr Assad's forces have been hitting back at rebel advances with bouts of heavy shelling, particularly along the eastern ring of suburbs outside Damascus, where rebels are dominant.
A Syrian security source said the army was planning heavy offensives in northern and central Syria to stem rebel advances, but there was no clear sign of such operations yet.
Rebels seized the Palestinian refugee district of Yarmouk earlier this week, which put them within 3 km of downtown Damascus. Heavy shelling and fighting forced thousands of Palestinian and Syrian residents to flee the Yarmouk area.
But rebels said today they were negotiating to put the camp - actually a densely packed urban district - back into the hands of pro-opposition Palestinian fighters. There are some 500,000 Palestinian refugees and their descendants living in Syria, and they have been divided by the uprising.
Palestinian factions, some backed by the government and others by the rebels, had begun fighting last week, a development that allowed Syrian insurgents to take the camp.
Despite warnings of continued violence, a video released by activists today showed dozens of people returning to Yarmouk. Most of the people in the footage were men, suggesting entire families may not be venturing back yet.
"There are still negotiations going on between the Palestinians and the rebels. The rebels want control of the checkpoints to be sure they can keep supply routes open to central Damascus," said a rebel who asked not to be named.
"Palestinians want their fighters to run the checkpoints so the army will stop attacking and people can go home. But we are worried there are government collaborators among them."
The fighter said rebels were looking to ensure their Palestinian allies could keep open access for rebels in Yarmouk, which they have described as a gateway to central Damascus.
Elsewhere, Syrian insurgents took over an isolated border post on the western frontier with Lebanon earlier this week, local residents told Reuters today.
They said around 20 rebels from the Qadissiyah Brigade overran the post at Rankus, which is linked by road to the remote Lebanese village of Tufail.
Video footage downloaded on the Internet today, dated December 16th, showed a handful of fighters dressed in khaki fatigues and wielding rifles as they kicked down a stone barricade around a small, single-storey army checkpoint.
"This is the end of you, Bashar you dog," one of the fighters said. The remains of two army trucks, which the rebels said had been blown up, stood nearby on a single track dirt road crossing a flat brown plain between snow-capped mountains.
The rebels already hold much of the terrain along Syria's northern and eastern borders with Turkey and Iraq respectively.
Syrian interior minister Ibrahim al-Shaar arrived in Lebanon yesterday for treatment of wounds sustained in a bomb attack on his ministry in Damascus a week ago.
Lebanese medical sources said Shaar had shrapnel wounds in his shoulder, stomach and legs but they were not critical.
The Syrian opposition has tried to peel off defectors not only from the army but from the government as well, though only a handful of high-ranking officials have abandoned Dr Assad.
But the conflict has divided many Syrian families. Security forces arrested today an opposition activist who is also the relative of vice president Farouq al-Sharaa, the Syrian Observatory said. The man was arrested along with five other activists who are considered pacifists, it said.
Sharaa, a Sunni Muslim who has few powers in Dr Assad's Alawite-dominated power structure, said earlier this week that neither side could win the war in Syria. He called for the formation of a national unity government to solve a crisis that has killed more than 40,000 Syrians.
Reuters