ODESSA, July 21 - Ukrainian protesters said Monday they had blocked NATO warships from participating in a military exercise in the Black Sea.

The Bratstvo, or Brotherhood, a leftist group, issued a press release Monday saying its members had moved boats into positions blocking the exits from the port of Odessa, preventing NATO ships from participating in the Sea Breeze 2008 exercise, RIA Novosti reported.

The left-wing group said three of its boats were detained, but the others continued the "blocking operation."