"We watch all submarine activity, not concerned about it," Mattis said on Tuesday when asked about Russian submarine activity spiking in the North Atlantic Ocean.
According to media reports, Chinese navy ships and Russian submarines have increased their activity in the North Atlantic Ocean. The Russian submarines are speculated to be attempting to interfere in underwater communications between North America and Europe.
READ MORE: Russian Submarine Conducts Salvo-Launch of 4 Ballistic Missiles for 1st Time
Previous month, a report suggested that USS Harry Truman aircraft carrier deployed to Atlantic waters from the Mediterranean Sea allegedly as a response to the reported increasing prevalence of Russian submarines off the United States’ east coast.