WASHINGTON - US President Barack Obama on Wednesday ordered sanctions against Syrian President Bashar al-Assad, his deputy, the prime minister and several other senior government officials.

Related readings:  'Catastrophic' picture emerges of Syrian town  Syrian official says unrest almost over  Syrian tanks shell towns, at least 19 killed  Hundreds protest US intervention in Syrian affairs

Obama said in his executive order that the additional steps were taken in response to Syrian government's "continuing escalation of violence against the people of Syria -- including through attacks on protesters, arrests and harassment of protesters and political activists, and repression of democratic change, overseen and executed by numerous elements of the Syrian government."

Under his order, Syrian President al-Assad, Vice President Farouk al-Shara, Prime Minister Adel Safar, Interior Minister Mohammad Ibrahim al-Shaar, Defense Minister Ali Habib Mahmoud, Head of Syrian Military Intelligence Abdul Fatah Qudsiya and Director of Political Security Directorate Mohammed Dib Zaitoun are put under US sanctions effective on Wednesday noon, under which their assets on US soil are frozen.

Obama also authorized his secretaries of treasury and state to target more senior Syrian officials and entities for sanctions.

On April 29, Obama put al-Assad's brother Mahir and cousin Atif Najib under sanctions along with Ali Mamluk, director of Syria's General Intelligence Directorate (GID), the GID and the Iranian Islamic Revolutionary Guard Corps Qods Force for their role in violence against protesters in Syria.

Syria has sent troops and tanks in many cities to quell unprecedented violence that coupled with anti-government protests. Syria blamed the unrest on armed terrorist groups and foreign conspiracy.

Additional US sanctions came one day before Obama is scheduled to deliver a speech on the events in the Middle East and North Africa and US policy in the region.