KIEV, Ukraine — Ukraine’s interior minister says three pro-Russian militants have been killed and 13 wounded after Ukrainian troops repelled an attack on a national guard base in the Black Sea port of Mariupol in the southeast part of the country.

Interior Minister Arsen Avakov said in a statement Thursday that a crowd of around 300 men, armed with Molotov cocktails, attacked the base late Wednesday but were repelled by the national guard and police. Avakov said 63 people had been arrested as a result of the operation and that most of the attackers were disarmed.

A well-armed, Russia-backed insurgency has sowed chaos in eastern Ukraine in the past weeks. Militants have seized police stations and administrative buildings in at least 10 towns in the region, including Mariupol.