Oil giant Royal Dutch Shell said on Monday it was selling its landmark London Shell-Mex House building to privately owned U.S. property group Witkoff Group. Shell UK did not give terms of the deal but recent British media reports said New York property baron Steven Witkoff was offering approximately $288 million. Shell said it intended to mostly vacate the art deco building on the Strand, overlooking the River Thames, by the end of the year. The decision to leave the company's British head office building, built in 1931, was first announced a year ago as Shell aimed to cut costs following the slump in oil prices. Shell-Mex housed some 2,000 staff working for Shell's UK and international operations.