In a statement on its website, Bahrain's interior ministry said Qatar had seized three Bahraini boats with 16 aboard in the past two days.
Coast Guard commander Ala Siyadi said in the statement that this took to 15 the overall number of boats seized and 20 the number of fishermen.
The Bahraini authorities did not specify when the other four people were detained, but the ministry said some boats had been seized in 2009.
The gas-rich emirate flatly rejects the allegations and the diplomatic row, the worst seen in the Gulf for decades, shows no signs of abating.