Syria's opposition umbrella group have met in a bid to name a prime minister-in-exile, a day after Syria rejected the idea that President Bashar al-Assad will be overthrown.
The diplomatic developments came on Sunday as five members of one family were killed in government air attacks on a village in Damascus province, according to a watchdog.
The National Coalition, which many Western and Arab powers recognise as the sole representative of the Syrian people, was discussing the idea of a government-in-exile in Istanbul, Turkey, but differences have emerged over who should lead the new executive, an opposition official told the AFP news agency.
In-depth coverage of escalating violence across Syria
"The US continues to have the president's departure as a condition of regime change, ignoring the fact that the captain of a capsized ship does not jump into the first boat," he said.
"A proposal was made to name Riad Hijab but it has run into much criticism," the official said on condition of anonymity.
Hijab, a former prime minister in the Assad regime, defected last August and has worked closely with Turkish leaders to help restructure the fragmented Syrian opposition.
The opposition bloc, which has called for the establishment of an interim government with full executive powers in rebel-held areas inside Syria, is due to meet on January 28 in Paris, Laurent Fabius, French foreign minister, said.
Defending the presidency
Earlier, Walid Muallem, Syria's foreign minister, struck a defiant tone, telling state television late on Saturday that those who demand Assad's removal wanted only bloodshed in the country.
"Nobody can afford to undermine the presidency - it is unacceptable," he said.
His statements came amid reports that Assad's mother, Anisa Makhluf, had left Syria and joined her daughter in Dubai, Syrian expatriates in the United Arab Emirates and an activist said on Sunday.
Makhluf's "departure from Syria is another indication of Assad losing support even from within his family", Ayman Abdel Nour, head of the newly formed group Syrian Christians for Democracy, said.
Analysts say Assad is increasingly relying on the tight-knit circle surrounding him, which includes Maher, his only brother still alive and who commands the army's notorious Fourth Brigade.
Meanwhile, a senior aide to Iran's supreme leader warned against the overthrow Assad, saying his fate was a "red line", in one of the Islamic state's strongest messages of support for the Damascus government.
Iran has steadfastly backed Assad's rule since an uprising against his rule began almost two years ago and regards him as an important part of the axis of opposition against arch-foe Israel.
"If the Syrian President Bashar al-Assad is toppled, the line of resistance in the face of Israel will be broken," Ali Akbar Velayati, who is seen as a potential contender in Iran's June presidential election, said in an interview broadcast on Sunday.
"We believe that there should be reforms emanating from the will of the Syrian people, but without resorting to violence and obtaining assistance from the [United States of] America."
The developments come as John Ging, director of the UN Office for the Co-ordination of Humanitarian Affairs (OCHA), attempts to assess Syrians' humanitarian needs.
Ging, who has been in the country since Friday, aims to assess how much humanitarian help is needed in Syria, where an estimated four million people, half of them displaced, are in need of emergency assistance.
The OCHA mission was received on Sunday by Faisal Mekdad, deputy foreign minister, and then travelled to Homs, even though a watchdog group reported government raids on besieged districts of the city.
In Damascus province, a couple and their three children were among nine civilians killed in air strikes on a village, while three people including a child died in shelling northeast of the capital, the Syrian Observatory for Human Rights said.
The Britain-based watchdog also reported one man killed by a sniper amid artillery shelling and warplane raids on Daraya, a strategic town next to the Mazzeh military airport, east of Damascus.
Al-Watan, a pro-government newspaper, said "terrorists on the outskirts of Daraya ... have appealed for help after being hit very hard by the Syrian army, which destroyed several of the hideouts where they barricaded themselves".
It said the army would press on with a ground operation to "root out the remaining terrorists".