U.S. crude oil fell on Thursday as the U.S. dollar strengthened on European debt woes.

After Moody's cut Spain's credit rating to Aa2 from Aa1 with a negative outlook, the euro on Thursday tumbled near 1 percent against the dollar. The European debt problems came back to the central stage.

The dollar index, which tracks the dollar performance against a basket of currencies, rose about 0.8 percent. A strengthening dollar weighed on oil prices.

And both in the United States and China, unexpected trade deficit also caused concerns about the global economic growth. Although economists said the Chinese deficit was probably temporary, it still weighed on the oil markets. The New York benchmark dipped to 100.62 dollars a barrel, the intraday lowest level.

In the late trading session, the losses were pared after reports said gunfire broke out in the world's largest oil producer and exporter Saudi Arabia. Concerns about the unrest spreading in North Africa and the Middle East lifted oil prices.

Light, sweet crude for April delivery fell 1.68 dollars to settle at 102.70 dollars a barrel on the New York Mercantile Exchange. In London, Brent crude also fell and last traded around 115 dollars a barrel.