Taiwan spotted two Russian warships off its eastern coast on Tuesday and sent its own aircraft and ships to keep watch, the island's defense ministry said.
In a statement late on Tuesday, the ministry said the two frigates sailed in a northerly direction off Taiwan's east coast and then "departed from our response zone" in a southeasterly direction off the port city of Suao, which is home to a major Taiwanese naval base.
Taiwan's military sent aircraft and ships to keep watch and activated shore-based missile systems, it added, without providing further details.
Russia's Interfax news agency reported on Tuesday that a detachment of ships of the Russian Pacific Fleet had entered the southern parts of the Philippine Sea to perform tasks as part of a long-range sea passage.
Taiwan has joined the United States and its allies in enacting wide-ranging sanctions against Russia following its invasion of Ukraine.
Democratically governed Taiwan, which China views as its own territory, has over the past three years regularly reported Chinese navy ships and air force aircraft operating around the island, as Beijing seeks to press its territorial claims.