After three pirates were killed during the Phillips incident, pirates have vowed to retaliate for their deaths. But Admiral Michael Mullen, chairman of the Joint Chiefs of Staff, told ABC's "Good Morning America" that:

"we're very well prepared to deal with anything like that."

The four ships seized since Sunday include:

The MV Sea Horse, a Lebanese-owned cargo ship, attacked and captured Tuesday by pirates in three or four speedboats.

The Greek-managed MV Irene E.M. was seized in a rare overnight attack on Monday night by pirates.

Somali pirates also hijacked two Egyptian fishing boats in the Gulf of Aden off Somalia's northern coast, with a total of 36 crew. It was not exactly clear if those ships were grabbed Monday or Sunday.

An analyst told NPR that the pirates made a major mistake with the Maersk Alabama. It was a U.S. ship, a U.S. crew, and U.S. cargo. Generally those three factors are diverse, making intervention by any one country unlikely.