President Ferdinand Marcos Jr. said on Monday the presence of a Russian attack submarine in the Philippines' exclusive economic zone (EEZ) in the South China Sea was "very worrisome". "That's very concerning.

Russia is surprised by the reaction of the Philippines to the passage of a submarine of the Russian Navy in the exclusive economic zone of this country. The vessel's stay was absolutely legitimate, Russian Foreign Ministry spokeswoman Maria Zakharova said at a briefing.

Tensions between Russia and the Philippines escalated as the Philippine military deployed a navy ship and air force planes to shadow a Russian submarine in the South China Sea last week, security officials said.