The head of the United Nations and a former U.S. president warned against allowing the war in Syria to spiral out of control, hours after President Donald Trump told Syrian ally Russia to "get ready" for retaliatory missile strikes.
UN Secretary-General Antonio Guterres said he called the ambassadors of the UN Security Council's veto-wielding powers late on April 11 -- the United States, Britain, France, Russia, and China -- "to reiterate my deep concern about the risks of the current impasse."
Guterres said he "stressed the need to avoid the situation spiraling out of control."
Meanwhile, former U.S. President Jimmy Carter, in an interview with the Associated Press, urged Trump to "keep our country at peace and not exaggerate or exacerbate the challenges that come up with North Korea, in Russia, or in Syria."
The 93-year-old former president said that even one-time, conventional missiles like those Trump appears to be considering in response to an alleged chemical-weapons attack can be "a dangerous thing" that can spiral out of control when two nuclear powers are involved.
"I hope he realizes very profoundly, as I did, and as other presidents have done, that any nuclear exchange could involve catastrophe for all human beings," Carter told the AP.
Some top Russian officials, including Moscow's UN ambassador, have also urged caution and warned of "grave" consequences, while other top officials on both sides have said they expect "common sense" to prevail and prevent the situation from spiraling out of control.
Trump early on April 11 had suggested a missile strike on Syria might be imminent in retaliation for a suspected chemical-weapons attack in the town of Douma that killed at least 43 civilians on April 7.
Russia and Syria deny there was a chemical attack and have warned that any missile strike on Syrian President Bashar al-Assad's forces and facilities would be countered in kind.
"Russia vows to shoot down any and all missiles fired at Syria," Trump wrote on Twitter. "Get ready Russia, because they will be coming, nice and new and 'smart!' You shouldn’t be partners with a Gas Killing Animal who kills his people and enjoys it!"
In response to Trump's tweet, the Russian Foreign Ministry said: "Smart missiles should fly towards terrorists, not towards the lawful government" of Syria.
White House spokeswoman Sarah Sanders later said that Trump's national security team met on April 11 to discuss “a number of options" in response to the suspected chemical-weapons attack in Syria.
“We are still considering a number of those and a final decision on that front has not been made," she told reporters.
Sanders also said that Washington holds Russia and Syria responsible for the incident.
U.S., French, and British forces have positioned submarines and navy guided-missile destroyers in the eastern Mediterranean within striking distance of Syria in what appeared to be preparations for an attack, while Trump has repeatedly conferred with the leaders of both countries.
In London, British Prime Minister Theresa May said late on April 11 that all indications pointed to Syrian government responsibility for "a shocking and barbaric act" that could not go unchallenged.
May called ministers to a cabinet meeting on Syria on April 12, which media reports said was likely to lead to London joining in a military response to the suspected chemical attack.
Meanwhile, Russia and Syria claimed that Syrian government forces had taken full control of Douma, the site of the suspected chemical attack and the last rebel holdout in the Damascus suburb of eastern Ghouta that had been under opposition control for years.
"Today, a significant event in the history of Syria took place. The raising of the [Syrian] flag over a building in the town of Douma signified control over this town and consequently over eastern Ghouta as a whole," Russian Major-General Yuri Yevtushenko said on April 12.
The claim has not been independently verified.
The Syrian Observatory for Human Rights, a war monitor, said pro-government forces were emptying main airports and military air bases throughout Syria.
The Syrian military has also been repositioning some air assets to avoid possible missile strikes, U.S. officials told Reuters.
Earlier on April 11, Ali Akbar Velayati, a top adviser to Iran's supreme leader, said Tehran would "stand by Syria's government against any foreign aggression." Iran has been one of Syria's key allies.
The World Health Organization said that 43 people who died in the attack on Douma suffered "symptoms consistent with exposure to highly toxic chemicals" and more than 500 in all had been treated. In total, more than 70 people were killed during the attack, the WHO said.
Global stock markets fell on worries that what had been a seven-year civil war in Syria could escalate into an international conflict, while oil prices jumped to their highest levels in more than three years.
The UN Security Council is scheduled to meet on April 12 to discuss the escalation of rhetoric over Syria and threats of unilateral military action.