It was lunchtime on Monday in this frightened, divided city and the streets were emptying fast. As gunfire crackled ominously in the air, merchants pulled down their shutters, soldiers peered nervously over sandbagged positions and people scurried home down deserted alleyways.

If Homs is not a city already in the throes of a full-blown war, between revolutionaries seeking to topple the Syrian regime and the pro-government forces determined to uphold it, then such a war does not feel far away.

On Monday, it seemed to come just a little closer, in Homs and beyond. An Arab League blueprint for President Bashar al-Assad to surrender power was rejected by the Syrian government, raising the stakes dramatically both for the beleaguered regime and for an increasingly emboldened opposition.

The unexpected Arab proposal also intensified pressure on the international community, which has struggled for months to formulate a coherent response to the Syrian crisis. By seeking U.N. Security Council endorsement for the plan, which envisages a transition of power similar to the one underway in Yemen, the Arab League appeared to open the door for broader international involvement in the Syrian crisis, including, perhaps, military intervention.

In Washington, State Department spokeswoman Victoria Nuland called the Arab move “really quite remarkable.” America’s priority now, she added, is to seek a U.N. Security Council resolution that would add to the pressure on Assad.

But there was still no indication that Russia is prepared to lift its objections to tougher action at the United Nations, which Moscow fears could lead to international military intervention in Syria, as happened in Libya.

Activist groups inside Syria also rejected the Arab blueprint. “What we heard is not even close to what the revolutionaries in Syria are demanding,” said a statement by the Syrian Revolution Coordinators Union. “We will persist until the fall of the regime, believing in God and trusting the heroic Free Syrian Army,” the group added, referring to the loosely organized rebel army that is claiming responsibility for a growing number of attacks against Syrian security forces.

Syrians on both sides of the widening schism predicted more violence, as the government digs in and the opposition seeks to exploit the advantage of the gradually hardening international resolve.

“Violence will escalate because this Free Syrian Army will think they have won a lot and that now it’s a piece of cake to take power,” said a Syrian journalist in Damascus who spoke on the condition of anonymity because of the sensitivity of the situation.

Omar Shakir, an activist in Homs contacted by telephone, said he expected the government to escalate the use of force. “Assad feels the world is against him, and so I think he will get mad and it will be very dangerous,” he said.

On a government-supervised visit Monday to Homs, which has emerged as the epicenter of the protest movement and also the fledgling armed rebellion, the dangers were vividly apparent. This once vibrant city, Syria’s third-largest, resembles a war zone, with earth mounds blocking streets and protecting government buildings, and sandbagged checkpoints dotting residential neighborhoods.

At the military hospital on the edge of the city, the toll that the burgeoning armed insurgency is taking on the Syrian security forces was clear. At a solemn ceremony on the hospital grounds, soldiers and police escorted three of their comrades, slain the previous day in ambushes, toward the cemetery nearby.

In the mortuary, doctors showed journalists the charred remains of four corpses stuffed into plastic bags, among 11 victims of a separate ambush the same day that had incinerated a minibus. In the intensive care unit, a soldier shot in the head that morning in the town of Qusair was fighting for his life.

The director of the hospital, Brig. Gen. Ali Assi, said 859 members of the security services had been killed in Homs since the uprising began in March, and that four to five typically had been killed each day. In the past three weeks, however, the daily average has climbed to 10 to 12 as the conflict appears to be intensifying, said orthopedic surgeon Hussein al-Habet.

“This is war,” he said. “And it is the worst kind of war in the military sense, because everyone in the world is against us and there are people fighting us from inside.”

The Homs Revolutionary Council, the leading opposition group in the city, claims that 2,052 people have been killed by government security forces in the past 10 months.

In the ancient Christian neighborhood of Hamidiyeh, residents seemed as confused as they were afraid. The conflict is rapidly taking on sectarian overtones, with majority Sunnis lining up behind the protesters and Shiite-affiliated Alawites rallying behind their Alawite president.

Khaldiyeh, one of two Sunni neighborhoods that has come under the control of the Free Syrian Army, is a short walk away, and Christians say they feel squeezed between two sides. Four have been kidnapped from the neighborhood in recent weeks. One was killed, even though his family paid a ransom.

Firefights have become a daily occurrence, and the shooting seems to be closing in, said a man working in a sweet shop who was too frightened to give his name. “It’s not a real war, but there are clashes every day and it’s getting worse,” he said. “We don’t know who is shooting who. It’s both sides. It’s very scary.”

Staff writers Colum Lynch at the United Nations and Joby Warrick in Washington contributed to this report.