Taiwan spotted two Russian warships off its east coast on Tuesday and sent its planes and ships to monitor them, the island’s defense ministry said, according to Reuters.

In a statement late Tuesday, the ministry said the two frigates sailed northward off Taiwan’s east coast before “leaving our response zone” in a southeasterly direction near the port city of Suao, home to an important Taiwanese naval base.

Taiwan’s military sent aircraft and ships to observe and activated missile systems from shore, it added, without giving further details.

The Russian agency “Interfax” reported on Tuesday that a detachment of ships of the Russian Pacific Fleet entered the southern parts of the Philippine Sea to carry out tasks as part of a long-distance sea crossing.

Taiwan has joined the United States and its allies in imposing sweeping sanctions against Russia following its invasion of Ukraine.

Democratically-ruled Taiwan, which China claims as its territory, has regularly reported Chinese navy ships and air force aircraft operating around the island over the past three years as Beijing tries to assert its territorial claims.