The UN's secretary general has said the Cold War is "back with a vengeance".
Antonio Guterres also warned about the dangers of escalation over Syria, reports BBC.
The US and its allies are considering launching missile strikes against Syria after a suspected chemical attack, an action which Russia - whose forces are there supporting the government- has said would risk starting a war.
Russia has accused the UK of faking an attack, an allegation Britain dismissed as a "grotesque, blatant lie".
The Cold War, which followed the Allied victory in World War Two, saw the US and its allies facing off for decades with the Soviet Union, of which Russia is the main successor state.
Mr Guterres delivered his warnings at the opening of a bad-tempered UN Security Council meeting.
"The Cold War is back with a vengeance, but with a difference," he said. "The mechanisms and the safeguards to manage the risks of escalation that existed in the past no longer seem to be present."
He urged countries to "act responsibly in these dangerous circumstances".
During the meeting:
- The Russian ambassador to the UN, Vassily Nebenzia, accused the US of using the suspected chemical attack as a pretext to overthrow the Assad government and "contain" Russia
- The US ambassador accused Syrian President Bashar al-Assad of using chemical weapons at least 50 times in seven years
- France's ambassador said Syria had gone "beyond the point of no return" and France would "shoulder its responsibility to end an intolerable threat to our collective security"
The US and France have both said they have proof the Syrian government attacked the Eastern Ghouta town of Douma last Saturday, but neither country has officially given further details.
On Friday, US state department spokeswoman Heather Nauert said: "We know for a fact that it was a chemical weapon."
When she was asked whether the US had proof the Syrian government was behind the attack, she said: "Yes."
The suspected attack, in which dozens of people reportedly died, was denied by Syrian President Bashar al-Assad's government.
Rescue workers from the Syria Civil Defence and the Syrian American Medical Society, which supports hospitals in rebel-held areas, said victims were found with foam coming out of their mouths, blue skin and lips, and corneal burns.