On Sunday March 13th it was announced that GCC troops would enter Bahrain. Around 1,000 Saudi forces and 500 UAE policemen were initially deployed. The deployment was officially at the invitation of the king. The government cited the GCC's Peninsula Shield agreement, which includes a clause stating that the GCC will defend any of its members against an external threat or external interference in internal affairs. It is the first time that GCC forces have been used in the face of an internal uprising, but the government justifies this by arguing that the protesters have a foreign agenda. Kuwait had a fierce internal debate over whether its forces should participate, and eventually compromised by sending three naval ships, in line with the principle of defence against external threats (while being unlikely to come into contact with any protesters).

Bahraini society became yet more polarised over the deployment of the GCC troops, largely reflecting sectarian identities. Al-Wefaq called the deployment an invasion. Meanwhile, government supporters have tended to argue that the GCC troops were needed because the country was on the brink of anarchy or civil war until they arrived. This view appears to conflate the deployment of the GCC troops with a U-turn in the tactics used by the Bahraini security forces, which took place at the same time. Having held back since the first raid on Pearl Roundabout, the focal point for protests, in mid-February, the security forces launched a second crackdown on March 16th to clear protesters from the area in which two policemen (according to the government) and five protesters (according to opposition groups) were killed and hundreds more were injured. The GCC forces are not believed to have been directly involved. The roundabout itself has since been bulldozed.