Two men have been arrested in connection with murder of prison officer David Black at the beginning of November.
The men, aged 34 and 42 were arrested in Coalisland and have been taken to Antrim police station for questioning.
Mr Black, a father-of-two from Cookstown, was killed in a motorway ambush on November 1 while driving to work at Maghaberry prison.
The arrests were made as it emerged the majority of inmates involved in the so-called dirty protest at the prison have ended their action.
Around 30 prisoners had been refusing to wash and were smearing excrement on the walls and floor of their cells as well as emptying urine into the prison landings.
The protest, which started last May, was in opposition to strip searches.
Around £500,000 has been spent cleaning the cells during the period.
Four men have already been arrested and released in connection with Mr Black’s murder.