Protesters in Bahrain denounced the arrival of foreign reinforcements from neighbouring Gulf states on Monday, calling the military intervention an "occupation" amid an uprising to oust the country's Sunni rulers.

Some 1,000 Saudi troops entered Bahrain by air, land and sea on Monday, joining a reported 500 police officers from the United Arab Emirates sent to stabilize the tiny Gulf kingdom while it faces an uprising from its Shia-majority population.

The CBC's Neil Macdonald said the message behind the task force's presence is clear: "If Shiite Arabs thinks they will topple or even force concessions from Sunni rulers, they're dreaming," he said.

The cross-border operation was perceived as a measure by Gulf Sunni dynasties to prop up Bahrain's monarchy, due to fears that arch-enemy Iran, a Shia-run power, could increase its influence over the region. Leaders of other Gulf nations worry that cracks in Bahrain's political foundation could have a ripple effect at home.

No apparent links have arisen between Tehran and Bahrain's opposition movement, but members of the Gulf Co-operation Council bloc reasoned it was their "common responsibility" to maintain order.

'We consider that any military force or military equipment crossing the boundaries of Bahrain … an occupation and a conspiracy against the people of Bahrain.'—Joint statement from opposition groups in Bahrain

"The Gulf leaders have tried to legitimize this," said Sami Alfaraj, director of the Kuwait Center for Strategic Studies. "They portray is not as intervention in an internal Bahrain dispute, but rather as an action against an external threat."

Upon learning of the deployment of security forces sent from the GCC, Bahraini opposition groups flooded into Pearl Square in the capital of Manama, blocking roads and condemning the arrival of outside military forces.

"No to occupation," demonstrators shouted in the streets.

The influx of military equipment and personnel into Bahrain was considered a statement of "an undeclared war by armed troops," opposition groups said.

Canada issues travel advisory

In a statement, a coalition of seven main opposition added: "We consider that any military force or military equipment crossing the boundaries of Bahrain … an occupation and a conspiracy against the people of Bahrain."

Of the six Gulf states comprising the GCC — Oman, Kuwait, Bahrain, Qatar, Saudi Arabia and the UAE — only the latter two nations have confirmed their contributions for deployments to Bahrain.

Bahrain police had already begun firing rubber bullets at protesters, but protesters fear live ammunition could be next.

The Canadian government is now advising against all travel to Bahrain while the political turmoil continues.

Bahrain's rulers have faced a month of revolt following a wave of rebellions for regime changes in the Mideast. Similar rallies in Oman, Kuwait and even Saudi Arabia have also begun to flare up.

In Washington, White House spokesman Jay Carney called on the foreign reinforcements to show restraint but stopped short of urging their withdrawal.

Dozens of Saudi military vehicles began rolling into Bahrain over the causeway linking the two countries. According to the Gulf Daily News, which is close to Bahrain's rulers, the forces are meant to protect critical national infrastructure such as power stations and oil facilities.

Shia Muslims account for 70 per cent of Bahrain's population, and citizens have long grumbled about discrimination by the ruling Sunnis, alleging they're often barred from good jobs.

With files from The Associated Press