by David Gura

At 12:45 p.m. ET, President Obama will hold a news conference at the White House. Before he takes questions from reporters in the East Room, the president is expected to announce new safety rules for offshore oil drilling, and to extend a moratorium on deep-water drilling.

Federal officials now say the oil spill in the Gulf of Mexico is the worst in American history, surpassing the Exxon Valdez spill in 1989. BP's latest attempt to stop the leak, by pumping thousands of gallons of drilling mud into it, may be working, Coast Guard Admiral Thad Allen told NPR this morning. But it is still too early to say for sure.

I'll live blog the president's news conference here, in the box below, as soon as the president steps up to the lectern. Once you hit "Play," you shouldn't have to refresh.