The US Vice-President, Joe Biden, has urged the Syrian President, Bashar al-Assad, to resign, saying his government was causing instability in the region.
Mr Biden was speaking on a visit to Turkey where he met Prime Minister Tayyip Erdogan.
He said the United States stood with the Turkish government in its calls for President Assad to step down.
Both nations are worried about Syria, where an eight-month crackdown on pro-democracy protesters has fanned fears of wider regional instability.
A US official said Syria was discussed only briefly and the two did not touch on what comes next there.
Meanwhile, an Arab League ministerial committee today slapped 19 Syrian officials with a ban on travel to Arab states and gave Damascus until Sunday to accept observers to monitor the unrest in the country.
Qatari Prime Minister Sheikh Hamad bin Jassim Al-Thani announced the new deadline for Syria to avoid sanctions after a meeting in Doha to discuss the measures decided against Damascus over its crackdown on protests.
The meeting issued a list of 19 Syrian officials banned from travel to Arab countries and whose assets are to be frozen by those states.
The Arab League last Sunday approved sweeping sanctions against Assad's government over the crackdown - the first time that the bloc has enforced such punitive measures against one of its own members.
23 killed in fresh violence
There have been further clashes in Syria which have left 23 people dead, including 11 civilians.
The fresh battles came just a day after the UN Human Rights Council urged tougher action against Damascus and condemned its "gross violations" of human rights.
Yesterday, an emergency meeting of the Human Rights Council passed a resolution "strongly condemning the continued widespread, systematic and gross violations of human rights and fundamental freedoms by the Syrian authorities."
But the Syrian foreign ministry rejected the resolution as "unjust" and said it was "prepared in advance by parties hostile to Syria”, in a statement carried by state news agency SANA.
In the northwestern city of Idlib, a focal point of anti-government protests raging since March, rebels clashed with loyalist troops near the provincial headquarters leaving 15 people dead, three of them civilians caught in the crossfire, a human rights group said.
An officer was among seven pro-regime soldiers and security service agents killed, the Syrian Observatory for Human Rights said. Five rebel troops also died in the fighting.
Also in Idlib, two protesters were killed and nine others wounded when security forces opened fire on an anti-regime rally in the town of Ariha, the Britain-based observatory said.
In the southern province of Daraa, one civilian was shot dead and five others wounded during a sweep by security forces in the town of Tafas.
The observatory said three more civilians were shot dead, one by a sniper, in the Sunni district of Bab Amro in the restive central city of Homs.
Two other civilians were killed by security forces in the town of Rastan north of Homs, the watchdog said.
In the town of Maarat Numan in Idlib province, meanwhile, the funeral for a 26-year-old man reportedly turned into a massive protest against the regime.
The unprecedented movement against Assad's regime has been spearheaded by peaceful demonstrators, but in recent months army deserters have formed a rebel Free Syrian Army which has inflicted growing losses on regular forces.
UN High Commissioner for Human Rights Navi Pillay said more than 4,000 people have been killed in the crackdown over the past eight months and tens of thousands arrested.
At least 12,400 people are reported to have fled the country.
