Up to 200 police officers in Northern Ireland have been involved in overnight raids targeting suspected drug dealers in Ballymena and South Belfast.
The operation, codenamed "Galiot", is intended to be a major crackdown on the North’s growing heroin trade.
A Police Service of Northern Ireland spokesman said officers had raided a number of houses and arrested sixteen suspects, ten in Ballymena and six in Belfast. The operation is to continue throughout the morning, he said.
The head of the NI drugs squad, Det Supt Judith Gillespie, said the operation was climax of a protracted investigation into heroin dealing.
"We've been gathering evidence and intelligence on certain people since October last year and it's our aim to severely damage the heroin and class A drug network in Northern Ireland," she said.
Operation Galiot was initially mounted to hit the supply of heroin in Ballymena, but during the investigation it was found it had extended to Belfast, she said.
