UN Secretary-General Antonio Guterres said on Thursday that there was a "flame of hope" in Syria following the fall of president Bashar Al Assad's regime but warned of significant challenges ahead.
He also underlined that Israel's widespread strikes on Syrian military infrastructure were "violations" of the country's sovereignty and called for them to cease.
"The Middle East is being consumed by many fires, but today, there is a flame of hope in Syria, and that flame must not be extinguished," he said.
"The people of Syria stand at the moment of history and the moment of opportunity, and that opportunity cannot be missed."
Following the fall of Assad's government, Israel unleashed air strikes on military sites, including the country's air force, navy and weapons stockpiles.
"Extensive Israeli air strikes continue. These are violations of Syria's sovereignty and territorial integrity, and they must stop," Guterres said ahead of a UN Security Council meeting chaired by US Secretary of State Antony Blinken.
Guterres also condemned Israel for pushing its forces into a UN-run buffer zone on its border with Syria following the fall of Assad.
"Let me be clear, there should be no military forces in the area of separation other than UN peacekeepers — period," he said.
"Those peacekeepers must have freedom of movement to undertake their important work. Israel and Syria must uphold the terms of the 1974 Disengagement of Forces Agreement which remains fully in force."
Guterres also raised the prospect of the international community making a first step towards easing sanctions in force on Syria.
"We should not forget that the sanctions were applied to the Assad regime. The situation has changed. Obviously, we are in the process of transition. And in the process of transition, I think there is work to be done by both sides," he said. "(But) there should be at least a first gesture — a first gesture showing solidarity with the Syrian people until conditions are met for all sanctions to be removed."
Earlier President Vladimir Putin said that the fall of Assad was not a "defeat" for Russia, claiming Moscow had achieved its goals in the country.
Assad fled to Moscow earlier this month after a shock rebel advance ended half a century of rule by the Assad family, marked by repression and allegations of vast human rights abuses and civil war. "You want to present what is happening in Syria as a defeat for Russia," Putin said at his annual end-of-year press conference. "I assure you it is not," he said, responding to a question from an American journalist.
"We came to Syria 10 years ago so that a terrorist enclave would not be created there like in Afghanistan. On the whole, we have achieved our goal," Putin said.
The Kremlin leader said he had yet to meet with Assad in Moscow, but planned to do so soon. "I haven't yet seen president Assad since his arrival in Moscow but I plan to, I will definitely speak with him," he said.
Putin was addressing the situation in Syria publicly for the first time since Assad's fall. Moscow is keen to secure the fate of two military bases in the country.
Agencies