The United States says military and diplomatic defections in Syria show a continuing "momentum building" against President Bashar al-Assad.
White House spokesman Jay Carney said Thursday that desperation is growing within Mr. Assad's government. On a trip to Cambodia, U.S. Secretary of State Hillary Clinton called for tougher U.N. action against Damascus.
The U.S. comments come after Syria's ambassador to Iraq defected this week and joined the opposition. Nawaf Fares is the highest-ranking Syrian official to switch sides since the uprising against Mr. Assad began 16 months ago. A general of Syria's Republican Guard defected last week.
In a lengthy message broadcast on Arab satellite channels, the former ambassador urged Syrian government officials and military personnel to follow his lead and join the opposition. "Where' he asked, 'is the honor of killing the people?"
The Latest Images From Syria (Click to Expand)
This image made from amateur video released by the Ugarit News shows a Free Syrian Army solider firing his weapon during clashes with Syrian government troops in Aleppo, Syria, July 24, 2012.
Free Syrian Army soldiers at the border town of Azaz, 32 kilometers north of Aleppo, Syria, July 24, 2012.
This image from amateur video released by the Ugarit News shows a Free Syrian Army solider driving a Syrian military tank in Aleppo, Syria, July 24, 2012.
This citizen journalism image provided by Shaam News Network purports to show a helicopter gunship flying a bombing run in al-Qalmoun, Syria, July 24, 2012.
This image provided by Shaam News Network shows smoke rising from Juret al-Shayah in Homs, Syria, July 23, 2012.
This citizen journalism image provided by Shaam News Network purports to show damage from heavy shelling of the al-Qadam district of Damascus, Syria, July 23, 2012.
A member of the Free Syrian Army points his weapon through a hole in a wall as he takes up a defense position in a house in Qusseer neighborhood in Homs, Syria, July 16, 2012.
A woman holds a child in front of their destroyed home in Tremseh, Syria about 15 kilometers northwest of Hama, July 14, 2012.
Free Syrian Army soldiers aim their weapons in Idlib, northern Syria, July 13, 2012.
This image made from amateur video from Hama Revolution 2011 purports to show a funeral for victims killed in Tremseh, Syria, July 13, 2012. (AP/ Hama Revolution 2011)
This image made from amateur video from Hama Revolution 2011purports to show families gathered around bodies of victims killed in Tremseh, Syria, July 13, 2012.
Members of the Free Syrian Army walk through Qusseer neighborhood in Homs, Syria, July 15, 2012.
Fares reportedly left Baghdad for the Kurdish autonomous region before announcing his defection. Iraqi authorities reported that he is on a visit to Qatar.
Clinton says Syrian defections show pressure is mounting on President Assad to give up power.
"The economy is in shambles," she said. "The regime is struggling to hold on to large parts of the country. So we do look to the Security Council and all of its members, including Russia, to join us in a serious resolution that gives special envoy Kofi Annan what he needs."
Diplomats emerged from a private meeting of the U.N. Security Council Wednesday clearly divided on the council's next action to end the fighting between government forces and the opposition.
Envoy Annan briefed council members via video link on the round of talks on Syria he held earlier in the week in Damascus, Tehran, and Baghdad. He later told reporters he had advised the council to speak with one voice, rather than divided, because a unified message is more powerful.
Annan also said he told the Security Council there should be consequences if the Syrian government and the opposition continue to ignore resolutions calling for an end to the fighting.
Clinton spoke with Annan this week and says she is encouraged that the U.N. and Arab League envoy is asking for a U.N. resolution that both endorses political transition and punishment for those who do not comply.
"The United States is determined to support him because our experience of the last year makes it absolutely clear that the Assad regime will not do anything without additional further pressure," she said.
Clinton woos China
Clinton met in Cambodia with Chinese Foreign Minister Yang Jiechi on the sidelines of a meeting of the Association of Southeast Asian Nations.
Russia and China have previously vetoed tougher U.N. action against Damascus on the grounds that it could lead to military intervention. Russia vowed on Thursday to continue that stance.
But Clinton says the United States and China agreed to do everything they can to back a political transition that is endorsed by all five permanent members of the Security Council.
"And we call on the Syrian military and business community to choose a democratic future rather than to cling to this crumbling regime," she said.
Defections depend on West
Hilal Khashan, who teaches political science at the American University of Beirut, says stronger action by the West would likely increase defections. Prominent Syrian officials have been slower to defect than their Libyan counterparts during last year's Libyan revolution, he said, in part because the West has been less keen to get involved in the conflict.
"The fact that an ambassador defected after 16 months means that the uprising is still gathering momentum," he said. "I think the main hurdle in Syria that has prevented major defections was the lukewarm reaction of the West. In Libya, the West interfered immediately and that accelerated the pace of defections," Khashan said.
In Syria on Thursday, witnesses say Syrian government troops fired mortar shells into fields and orchards separating the Damascus district of Kafr Souseh from a neighboring area. Analysts say it was the first time part of the capital has come under shell fire.
Syrian government forces also shelled a district in the embattled city of Homs for another day. Amateur video showed clouds of black smoke rising from burning buildings and badly damaged apartment blocks.
Stearns reported from Phnom Penh and Yeranian from Cairo.