Oil giant BP Plc's shares in New York sank further in early Monday trade after news that the U.S. Department of Justice was taking part in the investigation of the massive oil spill in the Gulf of Mexico.

BP shares in New York fell 6.4 percent to $48.84, bringing their drop to more than 18 percent since the close of trade on April 23. London stock markets were closed on Monday for a holiday.

U.S. Attorney General Eric Holder's comments that the Justice Department was involved in the probe raised the specter of criminal liability for BP in the oil spill spreading toward the Gulf Coast, after an explosion at a rig drilling its oil well on April 20.

Shares in other companies linked to the spill also weakened. Transocean Ltd , the owner of the drilling rig, saw its shares fell 3.3 percent to $70.06, Halliburton shares slipped 0.3 percent to $30.55, and Cameron International fell 2.7 percent to $38.40.

(Reporting by Matt Daily; editing by John Wallace)