Britain plans to propose a resolution at the United Nations on Wednesday demanding "necessary measures to protect civilians" in Syria from chemical weapons.

The proposal comes amid an international diplomatic flurry by the U.S. and Western powers as they decide how to unleash possible military action against President Bashar al-Assad.

The discussions come as a U.N. inspection team conducted an on-site investigation in suburban Damascus, where the alleged chemical weapons attack took place last week, leaving hundreds dead. It is the second inspection this week.

Russia, an Assad ally, says Britain's proposed U.N. resolution is premature. The Interfax news agency says Deputy Foreign Minister Vladimir Titov urged Britain to wait until U.N. inspectors presented their findings before considering any response.

U.N. Secretary-General Ban Ki-moon called on the U.N. Security Council to "find unity" on the situation in Syria. Mr. Ban said in a speech Wednesday in The Hague that the U.N. team in Syria needs time to do its work.

U.S. officials have said there is "no doubt" Syrian forces used chemical weapons. They also say President Barack Obama could decide on a response within days.

Syrian Foreign Minister Walid al-Moallem has denied his country carried out a chemical attack and challenged the U.S. and its European allies to show evidence.