"Syria's transitional government must hold accountable those responsible for the massacres against Syria's minority groups", he says in a statement, writes AFP.
Over 1,300 people are reported to have been killed along the Syrian coast since Thursday. The majority are said to be civilians from the Shia Muslim Alawite minority, according to the British-based Syrian Observatory for Human Rights (SOHR).
"The USA condemns the radical Islamist terrorists, including foreign jihadists, who have murdered people in western Syria in recent days", says Rubio.
He adds that the USA stands behind Syria's religious minorities.
"Christian, Druze, Alawite, and Kurdish communities", he says.
Sweden's Foreign Minister Maria Malmer Stenergard (M) calls the reports of killings and violence "terrible information".
"Civilians must be protected and all Syrians' rights respected. Syria needs a peaceful and inclusive political transition process that contributes to security, stability, and national unity. We are following the development closely and are in contact with our EU colleagues", she writes on X.
The UN High Commissioner for Human Rights Volker Türk condemns the events.
"The killing of civilians in coastal areas in northwestern Syria must stop immediately", he says in a statement.
Britain's Foreign Minister David Lammy writes on X that the authorities in Damascus must now "protect all Syrians and chart a clear path" towards justice.
