This is the first time Mr Assad has been targeted specifically by the international community for his government's violations of human rights of protesters demanding democratic reforms.
US President Barack Obama in April imposed sanctions on his brother Maher, his cousin and an intelligence chief.
The sanctions Obama signed yesterday against Assad and six senior officials (including Vice-President Farouk al-Sharaa, Prime Minister Adel Safar, Interior Minister Mohammed al-Shaar and Defence Minister Ali Habib) will not have any specific impact since the Syrian president does not have assets or interests in the United States, but it is highly symbolic because it is a rare step. For example, Washington has imposed sanctions on Muammar Gaddafi, but not North Korean leader Kim Jong-il.
Washington has not asked Assad to step down yet, but a US official said Mr Assad had a choice —lead a transition to democracy or leave. The decision also indicates that the US is not be satisfied by the measures Mr Assad has taken so far to solve the crisis.
Previously, Assad had given assurances that Syria would overcome the crisis. Last Friday, he apparently ordered his troops not to use weapons against expected protests following Friday prayers. Instead, four people were killed and many more were wounded.
Thousands of Syrians have fled to northern Lebanon and elsewhere, describing scenes of violence against civilians and demonstrators by the military and its supporters, especially in smaller towns, including systematic beatings and widespread arrests and other serious human rights violations.
In Tal Kelakh, residents have accused soldiers of going house to house to arrest protesters. In some cases, people "are resisting, preferring death to humiliation."
Human rights activists believe more than 850 people have been killed and thousands arrested even though the claims cannot be independently verified.
Prominent human rights lawyer Razan Zaitouna said the army and security forces had killed at least 27 civilians since moving into Tel Kelakh.
The Syrian government blames most of the violence on "armed criminal gangs", claiming that they have killed more than 120 soldiers and police.