President Ferdinand Marcos Jr. expressed concern on Monday regarding the presence of a Russian attack submarine within the Philippines‘ exclusive economic zone (EEZ) in the South China Sea, describing it as “very worrisome.”

“This is quite alarming. Any incursion into the West Philippine Sea, including our EEZ and baselines, raises significant concerns,” Marcos stated to reporters, referring to the area of the South China Sea that falls under Philippine jurisdiction.

On November 28, a Russian Kilo-class submarine was detected approximately 80 nautical miles from Occidental Mindoro, as confirmed by Navy spokesperson Roy Vincent Trinidad in a statement on Monday, which corroborated a report from the Philippine Daily Inquirer.

The Philippine navy frigate Jose Rizal established communication with the Russian submarine, which identified itself as UFA 490 and conveyed its intentions.

“The Russian vessel indicated it was waiting for better weather conditions before continuing its journey to Vladivostok, Russia,” Trinidad noted, without providing further details on its presence in the region.

Philippine naval forces accompanied the submarine to ensure adherence to maritime regulations, he added.

Attempts to reach Russia’s embassy in Manila for comment were unsuccessful.

Kilo-class submarines from Russia are recognized as some of the most stealthy submarines, having undergone continuous enhancements since the 1980s. In 2022, China and Russia proclaimed a “no limits” partnership during Russian President Vladimir Putin’s visit to Beijing, shortly before the onset of Moscow’s invasion of Ukraine. The two nations conducted live-fire naval drills in the South China Sea in July.

Rising tensions have emerged between Manila, a treaty ally of the United States, and Beijing over the past year, primarily due to conflicting territorial claims in the South China Sea. A ruling by an arbitral tribunal in 2016 determined that China’s historical assertions regarding the contested waters lack legal foundation, a verdict that Beijing continues to dispute.