Britain says it plans to introduce a U.N. Security Council resolution Wednesday that condemns the alleged chemical attack by Syrian forces and authorizes "necessary measures to protect civilians."
A United Nations team investigating the attack near Damascus resumed its work Wednesday, a day after postponing its on-site investigation because of security concerns.
U.N. Secretary-General Ban Ki-moon has called on the U.N. Security Council to "find unity" on the situation in Syria, and said the U.N. team in Syria needs time to do its work.
Mr. Ban said in a speech Wednesday in The Hague that the latest escalation in Syria has caused "horrendous casualties" and produced images unlike any the world has seen this century. He strongly criticized the use of chemical weapons, saying any deployment, at any time, under any circumstances would represent "an atrocious violation of international law."
Syria has denied carrying out a chemical attack.
As talk of a possible Western military response to the alleged attack grows, Russian Foreign Minister Sergei Lavrov is warning that foreign military intervention in Syria would destabilize the country and the region.
Russia's Foreign Ministry said Wednesday that Lavrov called for a political solution in a phone discussion with U.N.-Arab League envoy Lakhdar Brahimi, and that the two diplomats agreed all parties inside and outside Syria must act responsibly.
Brahimi told reporters in Geneva that international law clearly states military action cannot be taken without a decision by the Security Council. He also said it appears a chemical substance was used in Syria, calling the development unacceptable and "outrageous."
Brahimi has been working for a year to find a peaceful resolution to the crisis, which since March 2011 has left more than 100,000 people dead and millions more displaced.
He said the alleged chemical attack makes a U.S.-Russian effort to convene a Syrian peace conference even more urgent. Brahimi said both the U.S. and Russia remain committed to the conference, but that they understand the new developments will affect how all parties involved proceed.
In London, Prime Minister Cameron plans to discuss the situation in Syria with Britain's parliament on Thursday. He says any action would be a response to the use of chemical weapons, and not intended to draw Western powers further into the Syrian conflict.
Western powers and the Arab League have condemned what they say was clearly a chemical attack by Syrian forces last week that killed hundreds of people.
Syrian Foreign Minister Walid al-Moallem repeated his country's denial that it carried out a chemical attack and challenged the United States and its European allies to show evidence.
He said Syria's opponents are using the allegations as an excuse to attack, and vowed to strike back.
The Arab League has also condemned the alleged attack, blaming the Syrian government and demanding those responsible be put on trial.
U.S. officials have said there is "no doubt" Syrian forces used chemical weapons, and that President Barack Obama could decide on a response within days.