Syria's transitional prime minister has said it is time for "stability and calm" in the country, two days after longtime president Bashar al-Assad was toppled by rebels in a lightning offensive.
The rebels appointed Mohammad al-Bashir to run the country until 1 March, a statement said.
US Secretary of State Antony Blinken urged all nations to support an "inclusive" political process in Syria, saying the United States would eventually recognise a government if it meets such standards.
"Now it is time for this people to enjoy stability and calm," Mr Bashir told Qatar's Al Jazeera television in his first interview since being appointed.
A senior official told US broadcaster NBC that Mr Assad was in Moscow, after he fled Syria as an Islamist-led rebel alliance swept into Damascus on Sunday, ending five decades of brutal rule by his clan.
Abu Mohammed al-Jolani, the Islamist leader who headed the rebel offensive, had announced talks on a transfer of power and vowed to pursue former senior officials responsible for torture and war crimes.
His group, Hayat Tahrir al-Sham, is rooted in Syria's Al-Qaeda branch and is proscribed by many Western governments as a terrorist organisation, though it has sought to moderate its image.
Blinken calls for unity, inclusiveness
Mr Blinken said the future government of Syria should be "credible, inclusive and non-sectarian".
Laying out US priorities, Blinken said the new government must "uphold clear commitments to fully respect the rights of minorities" and allow the flow of humanitarian assistance.
The United States wanted the next government to "prevent Syria from being used as a base for terrorism", he added.
Although they no longer hold any territory in Syria, the jihadists of the Islamic State group remain active.
The Syrian Observatory for Human Rights war monitor said IS fighters killed 54 government troops after capturing them as they fled across the vast Syrian desert.
The UN envoy for Syria said the groups that forced Assad to flee must transform their "good messages" into actions on the ground.
"They have been sending messages of unity, of inclusiveness," Geir Pedersen said.
"What we need not to see is... that this is not followed up in practice in the days and the weeks ahead of us," he added.
EU foreign policy chief Kaja Kallas warned of the risks of sectarian violence and a resurgence of extremism. "We must avoid a repeat of the horrific scenarios in Iraq, Libya and Afghanistan."
Syria's nearly 14-year civil war killed 500,000 people and forced half the country to flee their homes, millions of them finding refuge abroad.
Mr Jolani, who now uses his real name Ahmed al-Sharaa, vowed: "We will not hesitate to hold accountable the criminals, murderers, security and army officers involved in torturing the Syrian people."
The fall of Assad has sparked a frantic search by families of the tens of thousands of people held in his security services' jails and detention centres.
As they advanced towards Damascus, the rebels released thousands of detainees, but many more remain missing.
Syria's White Helmet rescuers called on Russia to pressure Mr Assad into providing maps of secret jails and lists of detainees as they race against time to release prisoners.
A large crowd gathered yesteday outside Saydnaya jail, synonymous with the worst atrocities of Bashar al-Assad's rule, to search for relatives, many of whom had spent years in captivity.
"I'm looking for my brother, who has been missing since 2013. We've looked everywhere for him, we think he's here, in Saydnaya," said 52-year-old Umm Walid.
Crowds of freed prisoners wandered the streets of Damascus, many maimed by torture, weakened by illness and emaciated by hunger.
The United Nations said whoever ended up in power in Syria must hold Mr Assad and his lieutenants to account.
UN investigators who for years have been gathering evidence of horrific crimes called Mr Assad's ouster a "game-changer" because they will now be able to access "the crime scene".
While Syrians were celebrating Mr Assad's ouster, the country now faces enormous uncertainty, and it is unclear whether the dreams of democracy so many sacrificed their lives for will be realised.
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Further complicating prospects, the Israeli military said it had conducted hundreds of strikes on Syria over the past two days.
Mr Pedersen, the UN special envoy for Syria, called on Israel to stop.
"We are continuing to see Israeli movements and bombardments into Syrian territory. This needs to stop," he said.
But Israeli Prime Minister Benjamin Netanyahu warned Syria's new rulers that he would respond "forcefully" if they allow "Iran to re-establish itself in Syria" or if they permit the transfer of Iranian weapons or any other weapons to Hezbollah.
The Britain-based Observatory said Israeli strikes had "destroyed the most important military sites in Syria".
The monitor said the strikes targeted weapons depots, naval vessels and a research centre that Western governments suspected of having links to chemical weapons production.
Israel, which borders Syria, also sent troops into the UN-patrolled buffer zone east of the Israeli-annexed Golan Heights.
Israel backer the United States said the incursion must be "temporary", after the United Nations said Israel was violating the 1974 armistice.
The Israeli defence minister said the military had orders to "establish a sterile defence zone free of weapons and terrorist threats in southern Syria, without a permanent Israeli presence".
"Together with the prime minister, I have instructed the IDF (military) to establish a sterile defence zone free of weapons and terrorist threats in southern Syria, without a permanent Israeli presence," Defence Minister Katz said during a visit to a naval base in the northern city of Haifa.
He said it was in order "to prevent the establishment and organisation of terrorism in Syria".
Mr Katz said that Israeli naval missile ships destroyed the Syrian military fleet in an operation last night as part of a broad campaign to eliminate strategic threats to Israel.
It comes after Syrian security sources said that an Israeli military incursion into Syria reached about 25km southwest of Damascus, following air strikes on Syrian army and air bases overnight.
