FILE PHOTO: Head of the Security Service of Ukraine (SBU), Vasyl Hrytsak speaks during a news conference about Russian prisoners of war held in Ukraine, in Kiev, Ukraine, August 28, 2015. REUTERS/Valentyn Ogirenko

KIEV (Reuters) - A Ukrainian military counterintelligence officer was seriously wounded after Russian aircraft fired missiles at Ukrainian vessels on Sunday, the head of Ukraine’s state security service (SBU) said.

Ukraine and Russia have traded accusations after Russia fired on three Ukrainian ships then seized them. The confrontation prompted Ukraine to introduce martial law in some areas, citing the threat of a Russian land invasion. [nL8N1Y11BJ]

“According to the confirmed operational information of the SBU, one of the Russian attack aircraft used two unguided combat missiles against the Ukrainian boats, as a result of which one of the officers of the SBU was seriously wounded,” Vasyl Hrytsak said in a statement on Tuesday.

Russia has said SBU officers were among those captured. Hrytsak confirmed that and said the security officers were there supporting the military.

“The real surprise is the fact that against the two Ukrainian boats and the small tugboat, the Russians used six “FSB” (Russian Federal Security Service) and four naval vessels, as well as combat helicopters and airplanes of the Russian Federation Air Force,” he said.

He added that Ukraine’s security council was taking all necessary measures to secure the release of those captured.

The confrontation has exacerbated tensions already heightened after Russia’s 2014 annexation of Crimea from Ukraine and its backing for a pro-Moscow insurgency in eastern Ukraine.