Thousands of anti-government protesters have gathered in Moldova's capital and other towns demanding better governance and an end to widespread corruption.

Protesters massed in Chisinau on Sunday, with smaller protests in six other towns. There was a heavy police presence.

Authorities detained 13 suspected members of a paramilitary group this week who allegedly planning to attack the capital and a northern city with a majority Russian population, with the aim of creating a new separatist republic similar to the one in eastern Ukraine.

Interim Prime Minister Gheorghe Brega on Sunday called for increased security saying there were threats to Moldova's national security.

The Truth and Dignity non-governmental group has staged rallies since September, to protest against up to $1.5 billion that went missing from three banks before 2014 parliamentary elections.