Security specialists in the EU institutions are concerned that Shia-Sunni unrest in Bahrain has the potential to cause a sectarian conflict in the wider Arabian Gulf.

"What is happening in Bahrain is Sunni versus Shia, Saudi Arabia versus Iran. It's big powers facing off against each other in a small place. It's really explosive. We share the same concerns with the U.S. and with Russia," one EU source said on condition of anonymity.

"From a foreign policy point of view, it's a very big issue. We don't know where it will go," another EU contact noted, referring to a decision by Sunni powers Oman, Qatar, Saudi Arabia and the United Arab Emirates to send security forces to Bahrain to quell protests. "If Saudi Arabia and Iran become openly involved, it could become much more dangerous than Libya."

Writing in his blog, Swedish foreign minister Carl Bildt voiced similar concerns: "While there was most likely initially no Iranian interference, the opportunities for Iran to take advantage of the situation now undeniably grow."

Several EU countries, including the UK and Malta, have issued travel warnings for their citizens not to go to Bahrain or to leave the island nation as quickly as possible.

The UK Press Association reported that Britain has chartered commercial flights to get people out of the capital Manama, EUobserver reports.

The nervous atmosphere comes after masked Bahraini troops fired live rounds against protesters in the capital's Pearl Square on March 16. Six people, including three policemen, reportedly died in the fighting, with hundreds injured. Security forces overnight also swooped on the houses of opposition activists, taking three opposition leaders into custody.