The United States announced Thursday that four of Europe's five biggest oil companies would end their energy investments in Iran, a significant advance in the Obama administration's efforts to pressure the Iranian government to enter negotiations over its alleged nuclear weapons program, The Washington Post reports.

At the same time, U.S. officials said they were working to pressure China and other countries to bar their companies from filling the vacuum created by the departing Europeans.

Deputy Secretary of State James B. Steinberg said Royal Dutch Shell, based in Britain and the Netherlands; France's Total; Eni of Italy; and the Norway-based Statoil had committed to no further investments in Iran.

"These companies have provided assurances they will stop or are taking significant verifiable steps to stop their activity in Iran," Steinberg said. He also announced that the United States was slapping sanctions on a subsidiary of an Iranian oil company in Switzerland.

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