BEIRUT — Syria’s president defied mounting international pressure to end the bloody year-old crackdown on an uprising against him and said Tuesday he was determined to go on fighting what he called “foreign-backed terrorism.”

After a powerful American senator called for airstrikes on Syria, President Obama said unilateral U.S. military action against President Bashar Assad’s regime would be a mistake.

The United States said it is proposing a U.N. Security Council resolution demanding an end to violence in Syria, although Russia and China continue to support Assad.

The international outcry against Syria has been growing louder by the day. On Monday, U.S. Sen. John McCain called for airstrikes against Syria, saying the United States has a moral and strategic obligation to force out Assad. Obama has resisted calls to step into the turmoil in Syria to stop Assad’s crackdown on protesters. He told a news conference Tuesday that the international community has not been able to muster a campaign against Syria like the one in Libya that ousted Gadhafi.