Updated at 10:39 a.m. ET
BEIRUT - Syrian forces intensified a shelling assault on the restive city of Homs Monday, activists said, the third day of an onslaught of violence that began just as Russia and China blocked a U.N. attempt to end the regime's brutal crackdown on dissent. The U.S., outraged over the double veto, closed its embassy in Damascus Monday in a dramatic escalation of pressure on President Bashar Assad to give up power.
The Syrian military assault in Homs struck a makeshift medical clinic and residential areas, killing at least 23 people in the third day of a new offensive on the epicenter of the country's uprising, activists said. Another 10 people were reported killed elsewhere.
The U.S. evacuated all its diplomats from the country as Syrian forces intensified its assault on Homs. The decision to close the embassy is the most dramatic U.S. move so far after 11 months of a violent crackdown by Assad's regime.
The U.S. vowed to step up pressure on Assad to quit but ruled out military intervention. President Obama said a negotiated solution in Syria is possible and ruled out foreign military intervention.
In Cairo, Arab League chief Nabil Elaraby said he was "extremely alarmed and concerned" at the use of heavy weapons by regime forces. The League been an important diplomatic force trying to stem the bloodshed, and its proposal for a transition to democracy in Syria was the basis for the U.N. Security Council resolution that Russia and China blocked in a vote Saturday.
The government denied shelling Homs, however, and said "armed terrorist groups" were attacking civilians and police in several neighborhoods. The state-run news agency also said Monday that gunmen killed three soldiers and captured others at a checkpoint in the Jabal al-Zawiyah region of Idlib province, which borders Turkey.
Syria has blocked access to trouble spots in the country and prevented independent reporting, making it nearly impossible to verify accounts from either side as the conflict spirals out of control and turns increasingly violent.
Homs, which many refer to as "the capital of the Syrian revolution," has become a flashpoint of the nearly 11-month-old uprising against Assad. Several neighborhoods in the city, such as Baba Amr, are under the control of rebels.
The threat of both sides turning to greater force increased Saturday when Russia and China vetoed a U.N. Security Council resolution aimed at ending the bloodshed. Now regime opponents fear that Assad will be emboldened by the feeling he is protected by his top ally Moscow and unleash even greater violence to crush protesters.
On Saturday, Syrian forces killed up to 200 people in Homs the highest death toll reported for a single day in the uprising according to several rights groups. There was no way to independently confirm the toll.
While government forces have in the past used tanks and other weapons, the increased number of victims appear to have resulted from the indiscriminate use of artillery, according to the activists' reports.
"As of 6:30 this morning, the shelling intensified with a rate of one shell every two minutes," Baba Amr activist Omar Sheker said during Monday's bombardment.
The uprising began with mostly peaceful protests against Assad, but government forces responded with a fierce crackdown. Now, army defectors and others are taking up arms to fight back, raising fears of civil war.
China said Monday it was forced to use its veto because the vote was called too soon, before the parties could work out differences in the proposal. But China denied playing spoiler and said it wants to see an end to violence there.
China and Russia have drawn the wrath of the United States, Europe and much of the Arab world for the weekend veto. China says the resolution put undue emphasis on pressuring the Syrian government and prejudged the result of any dialogue between the parties in Syria.
"On the issue of Syria, China is not sheltering anyone nor do we intentionally oppose anyone. We uphold justice and take a responsible attitude," Chinese Foreign Ministry spokesman Liu Weimin said Monday.
Also Monday, an explosion ripped through a gas pipeline in Homs, the state-run news agency, SANA, reported. SANA blamed terrorists. The regime says terrorists acting out a foreign conspiracy are behind the uprising, not protesters seeking change.
The Local Coordination Committees activist group said Monday's shelling in Homs hit a makeshift clinic in Baba Amr, causing casualties.
At least 17 people were killed across the city on Monday, according to the LCC and the Britain-based Syrian Observatory for Human Rights.