The Russian navy has denied reports that two ballistic missiles failed to launch from a submarine during a military exercise in the Barents Sea. A spokesman for Russia's Northern Fleet said there had been no "unforseen incidents" during Tuesday's exercise.
But Russian news agencies quoted a Northern Fleet official as saying the launch had failed, apparently because of a satellite error.
President Vladimir Putin was on a submarine watching the manoeuvres.
The reported missile failure comes weeks before the presidential election, in which Mr Putin is widely expected to win a second term.
Interfax and Itar-Tass, quoting an unnamed navy officer, reported that a signal from a military satellite had blocked the launch. No further explanation was given.
The missiles had been due to take off from a nuclear submarine, the Novomosskovsk, with Mr Putin watching from another submarine, the Arkhangelsk.
Itar-Tass said the Novomosskovsk was to test-fire two ballistic missiles in succession at a practice target more than 5,000km (3,107 miles) away on the Kamchatka Peninsula in Russia's Far East.
The president's arrival at Severomorsk naval base, on Russia's Arctic coast, had received wide television coverage in Russia. Mr Putin was filmed wearing navy gear on Monday night as he chatted with sailors on board the Arkhangelsk submarine.
The planned manoeuvres had been described in the Russian media as the largest show of military might since Soviet times. Ten ships and six nuclear submarines had been due to take part.
In August 2000, just months into Mr Putin's term as president, a nuclear submarine, the Kursk, sank in the Barents Sea, killing 118 sailors.