TOKYO: U.S. Secretary of State Hillary Clinton said on Sunday Syria's opposition forces are growing more effective and the sooner the violence ends, the higher the chances of sparing the Syrian government from a "catastrophic assault."

It appeared clear that Clinton was referring to the possibility of Syrian rebels launching such an assault on state institutions - a court and a broadcaster have been recent targets - rather than to any outside intervention.

"The sooner there can be an end to the violence and a beginning of a political transition process, not only will fewer people die, but there is a chance to save the Syrian state from a catastrophic assault that would be very dangerous not only to Syria but to the region," Clinton said at a news conference.

Clinton was speaking in Tokyo after a meeting with Japanese Foreign Minister Koichiro Gemba. The two were meeting on the sidelines of an international conference on aid to Afghanistan.

"There is no doubt that the opposition is getting more effective in their defence of themselves and in going on the offence against the Syrian military and the Syrian government's militias. So, the future .... should be abundantly clear to those who support the Assad regime," Clinton added.

"The sand is running out of the hour glass."

In the United States, Republican Senator John McCain criticized Clinton and President Barack Obama for failing to show greater American leadership in the Syria crisis.

"The United States of America's performance so far has been shameful and disgraceful," McCain, the top Republican on the U.S. Senate Armed Services Committee, said on the CBS program "Face the Nation."

"We need to show first leadership. The president of the United States should be speaking out for the people of Syria," McCain said of Obama, a Democrat who defeated him in the 2008 U.S. presidential election.

McCain said he was not calling for American forces on the ground in Syria but that the United States should help arm Syrian rebels to make it a fair fight against Syrian government forces who have arms from Russia.

"We should get arms to them (rebels) so that we can balance the forces, it's not a fair fight, Russian arms are pouring in, Iranians are on the ground," McCain said.

McCain said the Syrian opposition has not been taken over by extremists, but that could happen if the conflict drags on. "The fact is that we know who to get arms to, we know that if they had a sanctuary or a safe zone that they could organize better," McCain said. AGENCIES