US Secretary of State John Kerry will make a statement on the situation in Syria at 12.30pm (1630 GMT), his office said Friday, as Washington prepared to launch missile strikes.
President Barack Obama has vowed that Bashar al-Assad's regime will be punished for a chemical weapons attack last week which reportedly killed hundreds of Syrian civilians.
US warships armed with dozens of cruise missiles are on standby in the Mediterranean, and France and the United States have said they are ready to launch strikes despite their failure to obtain a UN mandate for action.
Britain, which had initially planned to be part of the coalition, dropped out of the military planning on Thursday after British lawmakers voted to veto its involvement.
Assad has vowed to resist the intervention, and his allies Russia and Iran have warned that any Western attack would be a dangerous escalation.