"They were involved in activities incompatible with the laws of the country," the source said.
Protests against the ruling Communist Party's victory in Sunday's elections turned violent on Tuesday, with around 10,000 rioters taking control of the presidential residence and nearby parliament building. Some 170 police officers and more than 100 civilians were injured in the clashes.
The country's President Vladimir Voronin has accused Romania of inciting the violence in the capital and on Wednesday the Moldovan Cabinet approved the introduction of a visa regime with Romania and also expelled the country's ambassador over the disorder.
The capital was reported to be quiet overnight without any demonstrations or repeat of the protests in the capital that western media is dubbing the "Twitter Revolution," which along with the Internet and SMS texting played a key role in mobilizing people onto the streets.