Bahrain--Eyewitnesses have reported seeing an estimated 30 tanks being transported into Bahrain from Saudi Arabia on Monday night at around 6:45pm local time. The tanks were sighted along the King Fahd causeway, which links the small island-nation of Bahrain to Saudi Arabia.

Commuters traveling along the 25-km causeway were held up due to the presence of “15 tank carriers carrying two tanks each heading towards Bahrain.” Civilian eyewitnesses could not, however, confirm whether the tanks belonged to the Saudi military.

The presence of Saudi military hardware in Bahrain is considered highly unusual.

The development comes on the eve of yet another scheduled anti-government demonstration organized by the Bahraini opposition and protesters in Manama's Pearl Roundabout. 

Fears of Saudi intervention in the ongoing Bahraini uprising first came to the fore last week when unconfirmed reports emerged on Wednesday that Saudi officials had told US authorities that they were "prepared to intervene" in Bahrain should such a move prove necessary to protect Bahrain's embattled government. 

Tomorrow's mass protest will be the first to take place since the arrival to the country of controversial Shia opposition leader Hassan Mosheima from self-imposed exile.

Mosheima arrived on Saturday, using his first speech to call for national unity and to urge protesters to step up demands for the ouster of Bahrain's prime minister of 40 years, Sheikh Khalifa Al Khalifa.