BAGHDAD (Reuters) - Guerrillas fired mortar rounds into the center of Baghdad, hitting an area near the headquarters of the U.S.-led occupation authority in Iraq (news - web sites). Three mortar rounds thudded into the area where the complex is situated shortly before midnight on Thursday, witnesses said, ending a day punctuated with rocket and mortar attacks on hotels used by Westerners, embassies and an apartment block. Earlier, on what was a gloomy Christmas Day in the capital, a U.S. military spokesman said three or four rockets landed near the complex, once a palace of captured Iraqi leader Saddam Hussein...