BEIRUT: World leaders indicated they would not stand by to allow the “massacre” of Syrians in the country, as the Syrian opposition said they were bracing for a massive assault on the central city of Homs Friday, reporting thousands of regime forces and militiamen encircling the protest hub.

Influential former Saudi intelligence chief Prince Turki al-Faisal told a conference in Vienna he believed the Arab League was “not going to sit back and allow the continued massacre of the Syrian people.”

“Sanctions have been imposed. I think more measures will be undertaken in the near future,” Turki said.

He said while he believed President Bashar Assad was unlikely to step down voluntarily, Saudi Arabia was also unlikely to broker a transfer deal, similar to the one it negotiated with Yemen’s President Ali Abdullah Saleh.

Diplomatic efforts to resolve the crisis in Syria have stalled, with Assad rejecting a November Arab League peace plan calling for government forces to be withdrawn and Arab observers to be allowed into Syria.

Turkey also warned Syria it would act to protect itself if a Syrian government crackdown on protesters threatened regional security and unleashed a tide of refugees on its borders.

Turkish Foreign Minister Ahmet Davutoglu did not say what action Ankara might take, but indicated Turkey would act to insulate the region’s security from tumult in Syria.

“Turkey has no desire to interfere in anyone’s internal affairs. But if a risk to regional security arises, then we do not have the luxury of standing by and looking on,” Davutoglu told reporters in Ankara.

The United States meanwhile said it was “extremely concerned” by reports that Syria plans a large assault on the key city of Homs after leading opposition group, the Syrian National Council, issued an alert ahead of nationwide protests, warning the Syrian regime was planning “a security crackdown operation that may reach the level of a total invasion of the city.”

“We’re extremely concerned about what’s going on in the city of Homs. There are reports today that the government may be preparing a very serious new assault on the city of Homs in a very large-scale way,” U.S. State Department spokeswoman Victoria Nuland told reporters.

“It’s a perfect example for them to prove that they are not the propagators of this violence, and obviously they’ve chosen not to do so,” she said. “They are not going to be able to hide who’s responsible if there is a major assault.”She reiterated calls by the Arab League for Syria to let in monitors and also urged the regime to permit international media to travel in the country to see the situation first-hand. Arab League ministers will meet this weekend to mull a response to Syria’s Sunday request that the bloc lift sanctions as a precondition to allowing monitors in.

Britain also called on Syria to immediately withdraw its forces from the city.

Meanwhile, the U.N. chief Navi Pillay reiterated a request to allow human rights monitors into the country and said lives could have been saved if the Security Council had acted earlier over the Syria crackdown.

“Now it is more than 4,000. Lives could have been changed if action had been taken sooner. It is not for me to determine what kind of action, it is for the Security Council,” she said.

European members of the Security Council have called for Pillay to brief the 15-nation body next week and diplomats said “heated” talks on the proposal were held Friday.

In a statement Thursday, the SNC said Assad’s security authorities were using the pretext of what it called a “terrorist” attack on an oil pipeline Thursday to overrun Homs.

“The regime has tried hard to ignite the sectarian conflict using many dirty methods, which have included bombing and burning mosques, torturing and killing young men, and kidnapping women and children,” said the SNC.

“The regime also took a significant step ... in burning oil pipelines in the neighborhood of Bab Amro to blame what the regime calls ‘armed gangs’ in an attempt to crush the peaceful uprising on the pretext of a war on terrorism.”

Syrian state television Thursday aired confessions by “terrorists” bent on destabilizing the country by attacking security forces, killing and sabotage.

Witnesses on the ground in the central city have reported a buildup of troops and pro-regime “Shabiha” militiamen in armored vehicles who have set up more than 60 checkpoints, said the opposition group.

Activists group, the Local Coordinating Committees, reported 37 people killed Friday, including 18 in Homs alone. They said seven children, two women and four defected soldiers were among those killed by security forces.

Homs has become the epicenter of the Syrian uprising. Defectors from the army and some activists have taken up arms to fight the government and there are increasing reports of retributive sectarian killings. The LCC issued a report Thursday declaring the city a “crisis zone” and detailed a rise in sectarian incidents, kidnappings and reversed kidnappings.