On the heels of a U.S. indictment of Hamas (search) leaders, the State Department on Saturday issued an updated warning that Americans in the Middle East and North Africa could be targets of terrorist attacks.

"Anti-American violence could include possible terrorist actions against aviation, ground transportation and maritime interests, specifically in the Middle East, including the Red Sea (search), Persian Gulf, the Arabian peninsula and North Africa," the department said.

The federal indictment unsealed Friday in Chicago against a senior political leader of the militant Hamas group and two others "may be used as an excuse to target American citizens or American interests throughout the region," the alert said.

The indictment alleged that Mousa Mohammed Abu Marzook (search), deputy chief of the Hamas political bureau who now lives in Syria (search), and two others, who were arrested in the United States, used U.S. bank accounts to launder millions of dollars to support Hamas and pay for attacks against Israel (search) over 15 years. The U.S. government designated Hamas as a terrorist organization in 1995.

The State Department said credible information indicates terrorist groups seek to continue attacks against U.S. interests in the Middle East, including Westerners and oil workers in the Gulf region. It said increased security at embassies and consular offices had led terrorists to seek easier targets like public transportation, residential areas and public places where people congregate.

"Suicide operations, bombings, hijackings, kidnappings and targeted attacks resulting in death" are possible, the warning said. And while conventional explosives are the most immediate threat, "chemical or biological agents must be considered a possible threat."