BEIJING/VILNIUS, Nov 21 (Reuters) - China downgraded its diplomatic ties with Lithuania on Sunday, expressing strong dissatisfaction with the Baltic State for allowing Taiwan to open a de facto embassy there and raising tensions in a row that has dragged in Washington.

Beijing had already expressed anger this summer when Lithuania - which has formal relations with China and not Taiwan - allowed it to open an office in the country using the name Taiwan.

China's Foreign Ministry said in a brusque statement that Lithuania had ignored China's "solemn stance" and the basic norms of international relations.

No matter what Taiwan does, it cannot change the fact that it is part of China, the ministry said.

Taiwan's Mainland Affairs Council denounced China's "rudeness and arrogance", saying Beijing had no right to comment on something that was not an internal Chinese affair and purely a matter between Taiwan and Lithuania.

Taiwan's Defence Ministry later on Sunday reported two Chinese nuclear-capable H-6 bombers had flown to the south of the island, part of a pattern of what Taipei views as military harassment designed to pressure the government.