The Royal Navy in Britain has been monitoring Russian warships in the North Sea and has escorted one vessel skirting British waters, the Defense Ministry in London said on Tuesday, amid heightened tensions between the two countries.

The Defense Ministry said in a statement that it had noted an “upsurge” in Russian vessels in the region over the past few days, and that it sent the frigate St. Albans to escort the Russian warship Admiral Gorshkov through the North Sea as it neared British waters. A helicopter was dispatched to monitor two other Russian vessels.

“Britain will never be intimidated when it comes to protecting our country, our people, and our national interests,” Defense Secretary Gavin Williamson said in the statement.

It was not the first time Britain had taken such measures against Russian vessels. In January, the Royal Navy escorted a Russian aircraft carrier passing through the English Channel as it returned from Syria. In April, a patrol ship escorted a Ropucha-class landing ship through the English Channel, and there were other episodes involving Russian vessels in May and November.

The increased presence of Russian ships comes at a time of strained relations between London and Moscow. During a visit to Russia last week, the British foreign secretary, Boris Johnson, told his counterpart, Sergey V. Lavrov, that there was “abundant evidence” Moscow had meddled in foreign elections and had tried to interfere in British internal affairs.

Mr. Lavrov denied the accusations, and blamed Britain for an increase in tensions.

“It’s no secret that our relations are at a low point, and that’s not at our initiative,” he said.

The head of Britain’s armed forces, Air Chief Marshal Stuart Peach, has also warned of a “catastrophic threat” to the internet and global economy, with a growing risk of a Russian attack on the undersea cables that carry 97 percent of global communications and that transmit $10 trillion financial transactions each day.

Russia has increased patrols of attack submarines near undersea cables in the Atlantic, according to American officials, in what they say is only the most visible sign of Moscow’s renewed interest in submarine warfare and of its aggressive posture against NATO’s undersea dominance.