Syrian security forces have intensified their bloody siege against anti-government protesters, sending the three-day death toll above 130 as President Bashar al-Assad's international isolation deepens.

Rights activists and witnesses Tuesday said troops and pro-Assad “shabbiha” militiamen attacked the flashpoint city of Hama for the third day in a row, killing three more people and sending other residents fleeing for their lives. Most of the deaths in Mr. Assad's three-day military assault have occurred in Hama.

The United Nations Security Council is set to meet for a third day Wednesday to discuss possible actions to punish Syria. It has debated a European-drafted, U.S.-backed resolution that calls on Syria to stop assaulting its cities, implement political reforms and launch an impartial investigation into attacks on anti-government protesters.

Russia, a longtime ally of Damascus, suggested for the first time Tuesday that it would not oppose a U.N. resolution to condemn the violence. Moscow has long resisted any such measure by the Council, where it holds a veto.

Russia is pushing for a balanced response from the Council that would blame Syrian authorities and the opposition for the violence.

In Washington Monday, U.S. Secretary of State Hillary Clinton met with Syrian political activists in her first attempt to reach out to the expatriate opposition since the start of anti-government protests.

She encouraged the activists to work with those in Syria, and said the United States will continue to support the Syrian people. Clinton also said the U.S. is working on additional sanctions.

Syrian activists also called on U.S. President Barack Obama to call for Syrian leader Bashar al-Assad to step down. Mr. Obama said last month that Mr. Assad was “losing legitimacy in the eyes of his people” and had missed multiple opportunities to present genuine reforms.

Also Tuesday, the U.N. high commissioner for human rights warned Syria that “the world is watching” developments there. Navi Pillay bluntly criticized what she called Mr. Assad's efforts to shield the brutality of its crackdown by banning most foreign news coverage and preventing a U.N. fact-finding mission from visiting.

Italy also became the first European Union country to recall its ambassador from Syria, citing what it called the “horrible repression of the civilian population.”

Rights groups say Syrian forces have killed at least 1,700 civilians since the largely peaceful uprising began in March. The government has blamed much of the violence on what it says are terrorists and militants who have killed nearly 400 security personnel.