Syrian President Bashar al-Assad's regime is escalating its tactics against the opposition with bold, daylight attacks on its leaders, the US State Department said Friday.

"This is a clear escalation of regime tactics," State Department spokesperson Victoria Nuland told reporters.

Nuland meanwhile welcomed reported remarks from Russian President Dmitry Medvedev who told Assad to either reform or resign.

"That is very positive... I haven't seen the statement," she said.

"But as we have said, we want to see more countries join us not only in increasing the political and rhetorical pressure on the regime, but also tightening the economic noose," Nuland said.

"And there are more steps that can be taken by countries like Russia to up the pressure on Assad," she said.

Medvedev said three days after Russia and China sparked global outrage by jointly vetoing a UN resolution on Syria that he wanted to see an end to the brutal crackdown on protesters as much as Europe and the United States, AFP reported.