Japanese Defense Minister Nobuo Kishi voiced concern Tuesday over the recent modernizing of a Cambodian naval base with Chinese aid, during a meeting with his Cambodian counterpart.

Kishi urged Tea Banh to explain the rationale behind modernizing the Ream Naval Base, ASEAN sources told Kyodo News, at a time when China continues to expand its territorial ambitions in the East and South China seas.

The base, which is strategically located on the Gulf of Thailand, near the South China Sea, has been a source of geopolitical tension. The sea is where China's territorial claims overlap with some Southeast Asian countries.