Syrian tanks have stormed into the city of Hama, where residents have reported hearing loud explosions.

Activists and witnesses said Wednesday tanks are occupying a central square that has been a rallying point for protesters calling for the resignation of President Bashar al-Assad.

They say more than 130 people have been killed across Syria since Sunday, when the government stepped up its crackdown on dissent. Activists say most of the deaths occurred in Hama.

Meanwhile, the United Nations Security Council is meeting Wednesday for a third day of debate on a resolution condemning Syria government violence. The measure urges the government to stop its attacks on cities, implement political reforms and launch an investigation into the assault on 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 has been pushing for the Security Council to blame both Syrian authorities and the opposition for the violence.

In Washington Tuesday, 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 against Damascus.

Syrian activists also urged U.S. President Barack Obama to call for Mr. 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.

Rights groups say Syrian forces have killed at least 1,700 civilians since the 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.