MOSCOW — President Vladimir V. Putin on Wednesday dismissed the maritime clash between Russia and Ukraine as a criminal incident rather than the opening of a new front in the long-running conflict between the two countries, while a Russian court on the disputed Crimean peninsula sent a second group of captured Ukrainian sailors to jail.

“This is a border incident, nothing more,” Mr. Putin told an international business forum in Moscow when he was asked about the confrontation on Sunday when Russian ships fired on and seized three Ukrainian naval vessels in disputed coastal waters. It was his first public comment on the subject.

In Ukraine, President Petro O. Poroshenko enacted martial law for 30 days in 10 regions, mainly those bordering areas with a Russian military presence. Mr. Poroshenko has said that the sweeping provisions of martial law — which include the suppression of civil liberties — would only be invoked in the case of a Russian invasion.

“We need to rebuff the aggressor at any moment,” Mr. Poroshenko told troops at a Ukrainian training center, according to a statement on his website.