(CNN) -- U.S. Secretary of State Hillary Clinton said Sunday that "the days are numbered" for Syrian President Bashar al-Assad's regime.
"There is no doubt that the opposition is getting more effective in their defense of themselves and in going on the offense against the Syrian military and the Syrian government's militias," Clinton said during a press conference in Tokyo on Sunday.
And with a recent increase in defections from the al-Assad regime, "the sand is running out of the hourglass," Clinton said.
"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's a chance to save the Syrian state from a catastrophic assault that would be very dangerous not only to Syria but to the region," she said.
Clinton, speaking at a Tokyo conference on Afghanistan, acknowledged that a peace plan brokered by U.N.-Arab League special envoy Kofi Annan has thus far failed to stymie the bloodbath in Syria that has continued for 16 months. Annan arrived in Damascus on Sunday for talks with al-Assad, according to his spokesman.
But the violence raged on Sunday, as at least 43 people were killed across the country, said the Local Coordination Committees of Syria, a network of opposition activists. The dead included seven children and a woman, the opposition said.
Meanwhile, the Syrian military said exercises were under way after beginning Saturday. Live-fire operations were conducted "using missiles launched from the sea and coast, helicopters and missile boats, simulating a scenario of repelling a sudden attack from the sea," according to the state-run Syrian Arab News Agency (SANA).
The military exercises will involve land, sea and air forces, SANA said, "in order to test the combat readiness of the Syrian Arab Army and inspect its ability to carry out its duties in circumstances similar to possible combat conditions."
Asked to respond to Clinton's comments on Syria, Sen. John McCain of Arizona said, "I appreciate the remarks of the secretary of state. I admire her greatly. But the fact is, the United States has played no leadership role ... the United States of America performance so far has been shameful and disgraceful."
He said President Barack Obama "should be speaking out for the people of Syria. Second of all, we should get arms to them so that we can balance the forces. It is not a fair fight."
McCain said he believes al-Assad someday will go, but "my question to the secretary of state and the president of the United States is, how many more have to die before we take action to help these people with other nations?"
Despite the escalating chaos in Syria that led to the suspension of monitoring activities, the United Nations can continue to play a crucial role in the embattled country, Secretary-General Ban Ki-moon says in a report to be presented to the Security Council.
An advance copy of the report, which is circulating among Security Council members, was obtained by CNN ahead of a Wednesday briefing on Syria to the council by Annan.
The document admits the efforts to implement Annan's peace plan -- which includes a cease-fire and take measures to protect human rights -- have not worked.
In some places, the levels of violence are even higher today than they were before an initial cease-fire attempt, the report says.
"The situation has deterioriated significantly, and has become more militarized," Ban told journalists at the Japan National Press Club referring to Syria, according to the U.N.
The 300-strong U.N. team in Syria, whose mission is to observe and help implement the plan, has been unable to do its work as envisioned because of the current conditions, the document states.
Last month, the United Nations announced that it was pulling back its unarmed monitors because of escalating violence. Opposition groups slammed the international body for the suspension of its work.
Ban essentially put three options on the table: withdrawing the U.N. team; increasing its size or adding armed protection for them; or retooling the mission of the current team.
Ban elaborated the most on the idea to shift the strategy of the current U.N. team.
The team could retain its military observer capability and continue its fact-finding work, but with a limited scope in light of the violence in Syria, the report says.
In this scenario, the U.N. mission would move its personnel from the field back to Damascus, where it would focus on pushing forward the six-point plan to the Syrian government and the opposition.
"From a central hub in Damascus, the civilian component would continue liaison and dialogue with opposition and Government representatives in the provinces as security conditions allow," Ban writes.
Whatever the decision on the mission, "the international community's continued responsibility to Syria is a moral and political obligation," Gen. Robert Mood, commander of the U.N. mission to Syria, said in an open letter to the Syrian people Sunday. "We cannot and will not turn our eyes and ears away from your plight and will continue to work together, with you, to find new paths to political dialogue and peaceful resolution to the crisis."
The United Nations has said more than 10,000 people have been killed since the Syrian crisis began in March 2011. What started as peaceful protests against the regime spiraled into a bloody government crackdown and armed uprising.
One opposition group, the Syrian Observatory for Human Rights, said last week that more than 16,700 have been killed, including more than 11,000 civilians.
CNN cannot independently verify government and opposition claims of casualties because access to Syria by international journalists has been severely restricted.