Beijing's Foreign Ministry said it firmly opposes official interactions of any form with Taiwan by nations who have ties with .
Solemn representations is a literal translation of a Chinese term expressing diplomatic discontent.
At issue is a visit by Vice President Hsiao Bi-khim and Foreign Minister Lin Chia-lung, both of whom were welcomed to the Ventotene Conference for Freedom and Democracy in Italy.
China sees democratically governed Taiwan as its own territory, which it has.
Beijing has previously blasted Hsiao as an "independence diehard" and has criticized her Democratic Progressive Party (DPP) as a separatist outfit.
Taiwan's government has not sought formal independence but Beijing has, nevertheless, threatened to take the island by military force.
How Taiwan is planning to outlast China
Though Taiwanese foreign ministers travel abroad, it is rare for an official as high-ranking as the vice president to visit nations with ties to Beijing for fear of fallout for host countries.
Other prominent pro-democracy advocates such as , the wife of the late Alexei Navalny, and Belarus opposition leader Sviatlana Tsikhanouskaya are also in attendance.
The conference began on Thursday and is scheduled to wrap up on Saturday.
Taiwan minister to DW: 'You cannot be naive' with China
Edited by: Wesley Rahn
