After news last month of the first freedom of navigation operation to challenge China’s territorial claims in the South China Sea since president Trump took office, the US military has announced some more activity in the tense region.

Supersonic US Lancer bombers stormed over the disputed waters to “sharpen their combat skills” in a coordinated training operation with the USS Sterett destroyer, according to Air Force officials.

The 10-hour joint operation between the sea and air units is part of the Pacific Command’s continuous bomber presence program.

In response, the Chinese foreign ministry’s information office said (link in Chinese) that China “remained vigilant” and will “maintain effective monitoring” of the situation. The statement added that China’s military will “resolutely defend national sovereignty and regional stability.”