US President Barack Obama vowed to redouble efforts to force a change of regime in Syria as the UN Security Council struggled to agree on a resolution on Damascus's crackdown on dissent.
Obama said concerns about the crackdown on demonstrators by President Bashar al-Assad's forces had been "uppermost" in talks with visiting Jordanian King Abdullah II on Tuesday.
"We continue to see unacceptable levels of violence inside that country," Obama said.
"We will continue to consult very closely with Jordan to create the kind of international pressure and environment that encourage the current Syrian regime to step aside so that a more democratic process and transition can take place inside of Syria."
The US president thanked King Abdullah for being the first Arab leader to call publicly for Assad to go and for taking part in Arab League efforts to mitigate the crisis.
His comments came after Assad's government rejected a proposal to deploy Arab forces to halt unrest in Syria, where the UN estimates more than 5,400 people have been killed in the crackdown on democracy protests since March.
"Syria rejects the statements of officials of Qatar on sending Arab troops to worsen the crisis ... and pave the way for foreign intervention," the foreign ministry said.
"The Syrian people refuse any foreign intervention in any name. They will oppose any attempt to undermine the sovereignty of Syria and the integrity of its territory," the ministry said.
"It would be regrettable for Arab blood to flow on Syria's territory to serve known (interests)," a statement added, without elaborating.
In an interview with US television network CBS aired at the weekend, Qatar's emir, Sheikh Hamad bin Khalifa Al-Thani, said he favoured sending Arab troops to Syria to "stop the killing."
The Arab League is due to discuss the crisis in Syria on Saturday and Sunday, and is expected to discuss the future of its widely criticised observer mission.
Moroccan Foreign Minister Saad Eddin Othmani told AFP the meetings would "decide on how to continue the mission and what shape it should take," based on a report to be delivered by the observers' chief.
From its base in Turkey, the rebel Free Syrian Army called on the Arab League to "quickly transfer the case of Syria to the UN Security Council," in a statement signed by its leader Riyadh al-Asaad, a dissident colonel.
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The United Nations pledged this week to assist the Arab mission deployed in Syria since last month, saying it would start training the bloc's observers within days.
But the rebels demanded bolder action from the world body, urging it to "act quickly against the regime through Chapter Seven of the UN Charter to maintain peace."
Chapter Seven provides for UN forces to initiate military action, not simply act in self-defence.
Diplomats at the United Nations said experts from the 15 members of the Security Council held prolonged talks Tuesday on a proposed Russian resolution on Syria without getting closer to UN action on the bloodshed.
"There were more than four hours of talks but they only touched on the preparatory paragraphs," one Western diplomat said.
"We don't feel a real effort to close the gaps," commented another Western diplomat.
Western governments oppose the Russia text which they say wrongly equates security force violence with what they say is far less frequent armed action by the opposition.
The Syrian government's warning against the deployment of Arab troops came amid signs of stronger coordination between military and political opponents of Assad's regime.
The Syrian National Council, an opposition umbrella group, said it had opened a liaison office and hotline with the Free Syrian Army to follow developments on the ground.
The rebels claim to have gathered some 40,000 fighters under their command since anti-government protests broke out in mid-March.
Dissident tribal chief Nawaf al-Bashir warned that the rebels will be forced to intensify their armed struggle if the Security Council fails to act.
"If the Security Council does not take the necessary decisions, then Syria's revolutionaries and the Free Syrian Army will be forced to act for themselves," Bashir said in Istanbul.
In fresh violence on Tuesday, at least 20 civilians were killed, eight of them when a blast hit a minibus in Idlib province in the northwest, the Syrian Observatory for Human Rights said.
Meanwhile, the Arab League said it has decided to send 10 new observers to Syria on Thursday to replace 10 others who left the country citing personal reasons and to keep the number of monitors in the mission at 165.