U.S. President Barack Obama says he is “appalled” by Syria's use of violence against its own people, after rights activists said an army attack on the central city of Hama killed at least 80 people.

The White House released a statement Sunday that the “horrifying” reports out of Hama are demonstrating the “true character” of Syrian President Bashar al-Assad's government. Mr. Obama vowed the United States would increase pressure on Mr. Assad and work with others to isolate the Syrian government.

U.N. Secretary-General Ban Ki-moon called on the Syrian government to halt the use of force against its citizens immediately and respect their human rights.

A U.S. embassy official in Syria also condemned Sunday's attacks in Hama, calling it “warfare” against the Syrian people.

France too condemned the attack.

In addition to criticizing the assault, former Lebanese President Saad Hariri said “silence on the international and Arab levels” about the situation in Syria was only leading to the loss of more Syrian lives.