(CNN) -- The international sense of urgency over the Syrian crisis grew on Thursday, with U.S. Secretary of State Hillary Clinton calling for an arms embargo and other tough U.N. Security Council steps against the Bashar al-Assad regime.

Clinton suggested moving "very vigorously" toward a Chapter VII sanctions resolution, including travel and financial sanctions as well as the arms embargo, pressure that would coax the regime to comply with U.N. and Arab League envoy Kofi Annan's six-point peace plan. A Chapter VII resolution would provide for the use of force if needed.

Clinton, French Foreign Minister Alain Juppe and other top diplomats met Thursday in Paris about what to do if a week-old cease-fire in Syria fails.

"I think we are all here out of a sense of great frustration and outrage over what we see occurring in Syria," Clinton said. "We also are hopeful that despite the evidence thus far, the mission of Kofi Annan can begin to take root, starting with monitors being sent, but remembering that it's a six-point plan and that it is not a menu of options. It has to be a complete acceptance by the Syrian government of all six points."

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Also Thursday, U.N. Secretary-General Ban Ki-moon said violence has persisted and the Syrian government hasn't lived up to its own promise to withdraw troops from cities, a key element of Annan's peace plan.

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An advance team of U.N. observers is in Syria to check compliance with the cease-fire, with 30 unarmed monitors expected in the coming days. Ban called for an initial three-month observer mission to be expanded to 300 monitors in 10 locations and is asking the U.N. Security Council to authorize the expanded number.

Juppe said the failure of Annan's peace plan for Syria "would lead to civil war,"

"We cannot wait," Juppe told reporters. "Time is against us. We need to act quickly. Otherwise we'll have to see what other options are available to the Security Council and to the international community."

Russia and China, which have blocked the Security Council from taking action against the Syrian government, declined an invitation to the Paris meeting, the French foreign ministry said.

In the meeting, French President Nicolas Sarkozy urged nations to persuade Moscow and Beijing to drop their support for Syria's regime.

Ban said it appears violence "dropped markedly" after the truce began April 12, but government shelling of civilian areas, actions by armed groups, and other hostilities jumped again in recent days.

Thirty people, including two women and a child, were killed in Syria on Thursday, the opposition Local Coordination Committees of Syria said. Dozens more have been killed in the past few days.

The LCC featured a video posted online Thursday that it said showed a rocket hitting a high-rise in Homs, the scene of some of the worst violence since the Syrian uprising began more than a year ago. The resulting fireball was followed by thick black smoke.

The group also reported strong explosions in Homs from military artillery and a raid and arrest campaign in another part of the city, during which several people were arrested on charges of failure to appear for mandatory military service.

In the town of Hama, the group said, regime forces launched raids and destroyed homes, shops and the town's only hospital.

Annan's plan calls on both sides to end the violence, allow access to humanitarian groups, release detainees and begin a political dialogue.

Ban said in a letter to U.N. Security Council President Susan Rice, who is also the U.S. ambassador to the United Nations, that armed violence continues even though both the government and opposition say they're committed to ending it.

Annan's plan also says demonstrators should be able to protest peacefully, and while there was a restrained regime response to demonstrations a week ago, Ban said "there were nevertheless attempts to intimidate protesters, including reports of incidents of rifle fire by government troops."

There has also been no significant release of detainees, another point of Annan's plan, Ban said.

There also has been no substantive progress on providing humanitarian assistance, Ban said. The United Nations says 230,000 people have been displaced by the violence.

The lack of progress, Ban said, is unacceptable.

The United Nations and Syria on Thursday agreed on the function of the advance team of observers in Syria and the government's role while they are there.

Rice said the advance mission is an important test of whether Syria will permit the effective operation of a larger monitoring system.

She noted that the Security Council, in its Syria resolution Saturday, called on the Syrian government to make sure a larger monitoring mission could work unimpeded.

So far, she said, the monitors' movements have been restricted. Ban noted that in one instance, the government turned down the team's initial request to go to Homs, citing "security concerns."

Observers were in the Daraa province town of Harak on Thursday. After they left, regime gunfire killed two people and wounded dozens, the Local Coordination Committees said.

CNN cannot independently verify reports of violence and deaths as the government has severely restricted access by international media.

Syria has been engulfed in violence for 13 months as a national uprising has spread and the government has cracked down on peaceful protests. The United Nations estimates that at least 9,000 people have died since the protests began, while activist groups put the death toll at more than 11,000.

CNN's Elise Labott is reporting from Paris and Joe Vaccarello is reporting from the United Nations. CNN's Amir Ahmed, Tracy Doueiry and Joe Sterling in Atlanta contributed to this report.