Syria denounced as illegal Wednesday Washington's decision to close its embassy, while Russia said the move meant the United States had renounced its role as a peace sponsor.
But a Russian- and US-agreed deal for Syria to destroy its chemical arsenal made progress with the international watchdog announcing that nearly half of it had now been removed, including the entire stock of mustard gas.
Syria, meanwhile, announced that Israeli air raids on its territory earlier Wednesday killed one soldier and wounded seven.
The foreign ministry accused Washington of a "clear violation" of the Vienna Convention on Diplomatic Relations with Tuesday's decision to close Syria's embassy and two consulates, calling it an "arbitrary measure".
The decision "reveals the real objectives of US policy against the interests of Syrian citizens and is another step in the US support for terrorism and bloodshed in Syria", a ministry statement added.
The United States said it was closing Syria's embassy in Washington and consulates in Michigan and Texas and expelling remaining Syrian diplomatic staff.
Secretary of State John Kerry said the decision was taken because "the illegitimacy of the Assad regime is so overwhelming".
The State Department rejected the Syrian and Russian charges.
"We are abiding by not only the law but every aspect of the Vienna Convention on diplomatic relations," spokeswoman Jen Psaki said.
She said Washington remained "committed to and focused on seeing a political solution" despite the so-called Geneva peace talks remaining stalled since last month.
Moscow said it viewed the US decision with "concern and disappointment".
"By making such a unilateral move, our American partners in essence are depriving themselves of the role of cosponsor of the process of political regulation in Syria," the foreign ministry said.
Moscow accused Washington of prioritising regime change over the tasks of destroying Syria's chemical weapons and helping the country's people.
"Resolving these without direct cooperation with the Syrian government is impossible," the statement said.
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- Chemical disarmament progress -
Syria has now removed 45.6 percent of its most dangerous chemical weapons from the war-torn country, including its entire stock of mustard gas, the only agent in its arsenal that did not require mixing before use, the Organisation for the Prohibition of Chemical Weapons said.
Two shipments have been loaded aboard Norwegian and Danish vessels in Latakia over the past week for destruction outside Syria, the watchdog said.
Syria remains behind schedule for the destruction of its entire arsenal by June 30, but has increased the pace of removing its weapons after missing a series of key interim targets, the OPCW said earlier this month.
The June deadline was agreed by Russia and the United States last year as part of a plan to avert US-backed military strikes in the wake of deadly chemical attacks outside the Syrian capital blamed by the West on President Bashar al-Assad's regime.
Assad's military said Israeli raids early Wednesday killed one soldier and wounded seven in the Quneitra region on the Syrian side of the Golan Heights armistice line.
"We warn that these desperate attempts to escalate and exacerbate the situation in these circumstances by repeating these acts of aggression would endanger the security and stability of the region," the army command said.
The early morning air strikes took place 12 hours after four soldiers patrolling the Israeli side of the line were wounded, one severely, by a roadside bomb.
It was the third such incident in two weeks along Israel's northern frontier.
Elsewhere, Syrian state media said the army had seized a village in the Qalamoun region, where it is trying to sever rebel supply lines across the nearby Lebanese border.
"Army units took over Ras al-Ain, southwest of Yabrud, killing a large number of terrorists," state news agency SANA said, using the regime's term for the opposition.
The takeover comes four days after the fall of Yabrud, the last major rebel stronghold in the area.
Regime planes also raided Qudsaya northwest of Damascus, despite a months-long truce there, killing at least eight people, the Observatory said.
A security source denied to AFP that there had been any air strikes.
More than 146,000 people have been killed in Syria's war, and nearly half of the population has been displaced.