Vice Foreign Minister Kentaro Uesugi’s three-day trip to Solomon Islands comes on the heels of a visit by a senior U.S. delegation, who warned that Washington would take unspecified action against the South Pacific nation should the security deal with China pose a threat to U.S. or allied interests.

“We believe the deal could affect the security of the entire Asia-Pacific region and we are watching the development with concern,” Foreign Minister Yoshimasa Hayashi said Friday.

Uesugi, during his visit to the Solomon Islands, is expected to convey Japan’s concern about the security pact and discuss bilateral and regional issues.

Japan sees China’s increasingly assertive military activity in the East and South China seas as a threat in some of the world’s busiest sea lanes.

Japan is especially concerned about Chinese military and coast guard activity in the East China Sea near the Japanese-controlled Senkaku islands, which China also claims and calls Diaoyu.

Tokyo has in recent years significantly stepped up security cooperation and expanded joint drills with the United States and other Western partners, including Australia, India, France, Britain and Germany, that share its concerns about China’s growing influence.