"I would once again beseech you to refrain from the plans that you're now developing", Moscow's United Nations envoy Vasily Nebenzia said on Tuesday.
United States officials told Reuters that Washington was weighing a multinational military response.
French President Emmanuel Macron said any strikes would target Syrian government chemical facilities. Diplomats said votes were expected Tuesday on competing USA and Russian draft resolutions, but either power's text would be likely to be vetoed by the other. He also reaffirmed his support for an OPCW investigation.
President Bashar al-Assad's government and Russian Federation, his most powerful ally, said there was no evidence that a gas attack had taken place and the claim was bogus.
The World Health Organisation on Wednesday demanded "immediate" access to the victims of an alleged chemical attack in Syria, as the Kremlin urged countries to avoid taking action that could further destabilise the war-torn country.
The OPCW said its technical secretariat has asked the Syrian government to make the necessary arrangements for the deployment of a fact-finding mission.
The organization is made up of an worldwide team of investigators but it can not on its own determine who was responsible for the attack.
The UN session was the latest in a series of showdowns between Russian Federation and the United States and saw harsh words exchanged between the countries.
The bodies of the Iranians, described as military advisers, had been flown back to Iran and funerals would take place later on Tuesday, Tasnim said.
"We could find ourselves on the threshold of some very sad and serious events", he said.
US Ambassador to the UN Nikki Haley speaks during the United Nations Security Council meeting on threats to global peace and security and the situation in the Middle East April 9, 2018 in NY.
Will there be a military strike?
US Defense Secretary Jim Mattis on Monday accused Russian Federation of falling short on its obligations to ensure that Syria abandoned its chemical weapons capabilities.
"We are studying that situation extremely closely, we are meeting with our military and everybody else and we are making some major decisions over the next 24-48 hours", he told reporters and his cabinet.
Nearly exactly a year ago, the USA launched 59 Tomahawk cruise missiles at a Syrian government airbase in retaliation for another chemical weapons attack. Nor has Iran, which is deeply embedded in Syria alongside Assad's forces.
An American official said the USA was discussing with allies whether they would participate in a retaliatory strike.
A US Navy guided-missile destroyer, the USS Donald Cook, is in the Mediterranean.
The attack in Douma occurred late on Saturday amid a resumed offensive by Syrian government forces after the collapse of a truce with the Army of Islam rebel group.
"We received many patients who suffered from symptoms compatible with exposure to chlorine gas, high concentration chlorine gas", said Dr. Ahmad Tarakji of the Syrian-American Medical Society.
The White House sharply rejected any suggestion that Trump's own words about pulling USA troops out of Syria had opened the door for the attack, which killed more than 40 people, including children. The US circulated a revised draft resolution to the 15-member council, which it first put forward on March 1, amid a warning from Mr Trump that there would be a "big price to pay" for the suspected attack on Saturday.
A child is treated in a hospital in Douma, eastern Ghouta in Syria, after what a Syria medical relief group claims was a suspected chemical attack April, 7, 2018.