The U.S. has launched criminal and civil investigations into the Gulf of Mexico oil spill—the latest move by the Obama administration to show it is taking aggressive action amid bipartisan criticism of its response to the disaster.

"We have what we think is a sufficient basis for us to have begun a criminal investigation," said U.S. Attorney General Eric Holder Tuesday after meeting in New Orleans with state attorneys general and federal prosecutors from the region. Mr. Holder noted that 11 people died in the April 20 rig...