* U.S. naval destroyer joins Romanian, Bulgarian warships
* Signal of support after Russia's intervention in Crimea (Adds quote, details, background)
By Angel Krasimirov
SOFIA, March 12 (Reuters) - A joint exercise involving U.S., Bulgarian and Romanian naval forces in the Black Sea started on Wednesday just across the water from the Crimean Peninsula, where Russian military groups have seized control from Ukrainian authorities.
The United States says the naval exercises were planned before the crisis in Ukraine.
But they send a message of resolve to NATO members nervous about Russia's intentions in its former Cold War backyard, along with reconnaissance flights over Poland and Romania near the Ukrainian border and U.S.-Polish wargames.
The Bulgarian navy told Reuters the exercises started after a one-day delay due to unfavourable weather conditions. The Romanian navy declined to comment.
The USS Truxtun, a U.S. guided-missile destroyer and part of the U.S. Sixth Fleet headquartered in Italy, joined the manoeuvres with the Bulgarian naval frigate Drazki and three Romanian vessels in the Black Sea.
"This time the exercise has begun as planned," Bulgarian Lieutenant-Colonel Dimitar Titev said.
It was not expected to involve any live-firing.
Separately, Bulgaria's defence minister said that a joint BLACKSEAFOR naval exercise, that was to be led by Ukraine between March 28 and April 15, was cancelled.
BLACKSEAFOR was created in 2001 by Bulgaria, Georgia, Russia, Romania, Turkey, and Ukraine, who had agreed to form an international task force to enhance regional cooperation. (Writing and additional reporting by Radu Marinas,; Editing by Matthias Williams and Angus MacSwan)