WASHINGTON (CNN) - The Justice Department and the state of Alaska Thursday asked ExxonMobil to pay another $92 million for additional cleanup of shorelines in Prince William Sound and the Gulf of Alaska, which still contain oil from the 1989 Exxon Valdez oil spill.

The action was taken under a provision of the 1991 settlement, which allowed the government to reopen the agreement in 2006 to consider issues unforeseen at the time of the $900 million damage settlement.

The Justice Department said the need for the additional project stems from a series of 2001 studies that document the presence of residual oil from the spill along beaches in the oil spill area. The government said in a written statement it had not anticipated the oil would remain toxic and continue to affect the area.

"By sending our plan ... we are aggressively seeking to restore natural resource damages unforeseen at the time of the 1991 settlement," said Assistant Attorney General Sue Ellen Wooldridge.

Shares of Exxon (down $0.29 to $60.62, Research) edged lower in afternoon trade on the New York Stock Exchange.

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