U.S. consular services in Saudi Arabia remain closed five days after a threat surfaced against Western oil workers in the country, the U.S. embassy said.

The U.S. Embassy in Riyadh said consular services are suspended through Tuesday because of unspecified heightened security concerns at diplomatic outposts in Saudi Arabia.

"A new security message will be sent out as soon as consular services return to normal," an embassy statement read.

An embassy statement last week was specific to Western oil workers. The embassy said Friday it had information stating that terrorist groups may have plans to target oil workers, "possibly to include those U.S. citizens working for oil companies in the Eastern Province [of Saudi Arabia], for an attack and/or kidnapping."

The embassy provided no further information on methods, groups or timing of the attacks. The Saudi Interior Ministry in 2011 vowed to use "an iron fist" when violence in the Shiite-dominated Eastern province, the center of the kingdom's oil industry, erupted.

Flare-ups in violence in the past have involved disgruntled minority Shiites, who number around 2 million in the overwhelmingly Sunni kingdom. Riyadh's concerns in 2011 coincided with the start of the Arab Spring.

A February warning from the U.S. State Department said there may be risks to U.S. citizens traveling to Saudi Arabia. Westerners and Shiites were attacked in Eastern province in November.

The embassy warning follows a government takeover in Yemen by the Houthi movement, a Shiite group, and lingering regional threats from the group calling itself the Islamic State. Militants tied to the Islamic State in Libya were allegedly behind the abduction of four Filipino nationals earlier this month.