Updated 5:09 PM ET
(CBS/AP) UNITED NATIONS - U.S. Ambassador Susan Rice says the worst and most likely scenario for Syria is that Kofi Annan's peace plan will fail, spreading conflict and creating a major crisis across the region.
Rice said Wednesday after a closed-door briefing to the U.N. Security Council by one of Annan's deputies, that Syrian government was unlikely to immediately implement the Annan plan.
In her remarks, the ambassador said that the worse case alternative is that "the violence escalates, the conflict spreads and intensifies, it reaches a higher degree of severity, it involves countries in the region, it takes on increasingly sectarian forms, and we have a major crisis not only in Syria but in the region. The Council's unity is exploded, the Annan plan is dead, and this becomes a proxy conflict with arms flowing in from all sides."
If President Bashar Assad refuses to implement the peace plan, Rice said the U.N. Security Council should assume its responsibility and put additional pressure on Syria including sanctions. But Rice and other council diplomats said there is opposition from some members.
"I think there's no doubt that there are some who expressed great skepticism and some who said it's past time," said Rice. "So, that discussion continues, but I think it will continue not only here in New York but in capitals and in other contexts because the Syrian government has made commitments. It has blatantly violated those commitments. And I think it's quite clear, as we've said for many weeks, if they continued to do so, there should be consequences."
Rice's remarks come on the same day that the United Nations mission in Syria reported the discovery of 13 bodies with their hands tied behind their backs and evidence that some were shot at close range.
The latest sign of unchecked violence comes hours after U.N. and Arab League special envoy Annan left Damascus after calling the massacre of 108 people in Houla last Friday a tipping point in the Syrian crisis.
Annan's deputy, Jean-Marie Guehenno, told reporters after the U.N. Security Counci briefing that diplomats are deeply troubled by Syria's cycle of violence.
"I believe that in the council there's an understanding that any sliding toward full-scale civil war in Syria would be catastrophic, and the Security Council now needs to have that kind of strategic discussion on how that needs to be avoided," Guehenno said in Geneva after speaking to the New York-based Security Council by videoconference.
Guehenno also warned of the possibility of outside groups and terrorists taking advantage of the violence. "In any situation where there is a risk of civil war you have opportunistic actors, if one can say that, that can try to exploit that," he said.
Guehenno said he told the closed session of the 15-nation council that Annan's six-point peace plan to end the 15-month conflict must be fully implemented and that political process must include talks between the Syrian government and the opposition.
"It's very important that the Security Council be united in pushing for a political process," Guehenno said.
Annan's Deputy told the Security Council "that discussions were the only way out but that they were unlikely to happen as the uprising was now a revolutionary movement that was not going to stop," a Council diplomat told CBS News' Pamela Falk.
Dmitry Peskov, President Vladimir Putin's spokesman, was quoted as saying by the ITAR-Tass news agency Wednesday that "there can be no talk" about a shift in Russia's stance on Syria under foreign pressure.
Russia, along with China, has twice shielded Syrian President Bashar Assad's regime from the U.N. sanctions over his crackdown on protests. Syria is Russia's last ally in the region, providing Moscow with its only naval base outside the former Soviet Union and a top customer for Russian weapons industries.
The horrific images of the massacre in Houla, a group of villages near the battered city of Homs, have prompted the U.S. and at least a dozen other nations to expel senior Syrian diplomats.
The U.N. has accused Syrian forces of killing about 15 of the total 108 with shelling, but President Bashar Assad's regime denies opposition accusations that the rest of the dead were the victims of government-backed thugs going door to door and killing people execution-style.
Thirty-four women and 49 children, by the U.N.'s count, were stabbed or shot dead at point blank range.
Meanwhile, the Obama administration added new sanctions on a Syrian bank Wednesday as a top White House official said the U.S. wants to economically throttle the regime of Syrian President Bashar Assad and cut off salaries of pro-government thugs blamed for the grisly massacre in Houla.
The Treasury Department said the Syria International Islamic Bank has been acting as a front for other Syrian financial institutions seeking to circumvent sanctions. The new penalties will prohibit the SIIB from engaging in financial transactions in the U.S. and will freeze any assets under U.S. jurisdiction.
With the Obama administration unwilling at this point to pursue military options in Syria, the U.S. has relied heavily on economic sanctions as a means for pressing Assad to leave power. The United States will host other nations in Washington next week to look at ways to tighten international sanctions further.
"We are strangling the regime economically," White House deputy national security adviser Denis McDonough said.
David Cohen, Treasury undersecretary for terrorism and financial intelligence, said the toll taken by sanctions on Syria are "mounting day by day."
"They're drawing down their reserves without a ready means of replenishing those reserves," Cohen said.
The White House also blamed Iran for stirring up violence inside Syria and said Assad's fall would be a huge blow to Tehran. The United States is increasingly linking Syria and Iran rhetorically and tactically, applying economic pressure with and without help from the United Nations or other countries.
Iran is Syria's only staunch defender in the Middle East, and the Syria crisis has united Sunni Arab neighbors who see in Syria a way to weaken Iran, their main Shiite enemy.
"I won't speak for any other government," White House press secretary Jay Carney said in Washington. "I would simply say that it is our belief, and it's the belief that we express in these conversations, that supporting the Assad regime is placing oneself or one's nation on the wrong side of history."