Three Russian ships docked in Manila, the Philippines for a five-day port call on Monday aimed at improving navy-to-navy relations amid heightened tensions in the South China Sea.

The arrival of two anti-submarine ships Admiral Tributs and Admiral Vinogradov and a tanker ship is the sixth visit by the Russian navy under Philippine President Rodrigo Duterte who has distanced himself from treaty ally U.S. and sought closer ties with Russia. The Philippines and China have both laid claim to large portions of the South China Sea, with China building militarized artificial islands across the important shipping lane.