The United States is calling for Syrian President Bashar al-Assad to step down immediately, following the alleged assassination of a key opposition leader.

A White House statement strongly condemned Friday's killing of Mashaal Tammo, the spokesman for the Kurdish Future Party and a member of a newly formed Syrian opposition coalition. Activists say masked gunmen killed him at his home in the northern town of Qamishliwhen.

The White House warned Mr. Assad must step down now “before taking his country further down this very dangerous path.”

It also said the attacks demonstrate the Syrian regime's latest attempts to shut down peaceful opposition inside Syria, where thousands of protesters have been rallying for President Bashar al-Assad's departure.

The opposition leader was among eight people killed Friday in Syria, allegedly by security forces.

Earlier, Russian President Dmitry Medvedev said Mr. Assad needs to enact reforms or resign. But he added that Russia opposes foreign attempts to push Mr. Assad from power.

Russia had joined China on Tuesday in vetoing a draft U.N. Security Council resolution that condemned Syria for its crackdown on civilian protesters. The French news agency says anti-government protesters in the town of Dara'a trampled the Russian and Chinese flags on Friday.

Activists say another prominent opposition figure, former lawmaker Riad Seif, was beaten on Friday outside of a mosque in Damascus.

In another development Friday, Syrian Deputy Foreign Minister Faisal Mekdad blamed much of his country's deadly unrest on “terrorists.” He told the U.N. Human Rights Council that criminals have killed more than 1,100 people in Syria.

The world body, which is meeting in Geneva, is reviewing Syria's response to the pro-reform rallies.

The meeting is taking place a day after the U.N. raised its death toll from Syria's seven-month crackdown on dissent more than 2,900.