China downgraded ties with Lithuania to the level of charge d’affaires and is prepared to end diplomatic relations with the Baltic nation if need be, further raising tensions after Taiwan opened a diplomatic office there last week.

Lithuania is “walking back on political promises” made in a communique for establishing diplomatic links with China, the Chinese Foreign Ministry said in a statement Sunday. Hours later, Hu Xijin, the editor-in-chief of the Communist Party’s Global Times newspaper, wrote a dismissive message suggesting China would sever ties if Lithuania takes “further destructive action” on issues involving Taiwan.

“Lithuania is nothing but an itty-bitty country,” Hu said in a post on WeChat. “It’s just like a rat or flea at the feet of fighting elephants.”

China withdrew its ambassador from Lithuania in August in protest at the Baltic nation’s move to let Taiwan set up a representative office under the name of Taiwan, something that China deems disrespect to its sovereignty and territorial integrity.

China sees the democratically ruled island of Taiwan as part of its territory and has repeatedly voiced opposition to countries engaging in official contact with Taipei and vowed to take countermeasures. The “One China” policy is the political basis of relations between the two countries and the establishment of Taiwan’s office sets a bad international precedent, China’s foreign ministry said.

“We urge Lithuania to immediately correct this mistake and not to underestimate the Chinese people’s strong determination and ability to safeguard national sovereignty and territorial integrity,” it added.

The Lithuanian Foreign Ministry said it regrets China’s decision to downgrade diplomatic ties, reiterating that it respects the “One China” principle. The Baltic nation “has a right to expand cooperation with Taiwan, to accept and to establish non-diplomatic representations to ensure practical development of such ties,” like in many other countries, the ministry said in a statement.

“Lithuania has opened a representative office for practical cooperation,” Prime Minister Ingrida Simonyte said on Sunday. “But this is not a diplomatic representation office. I want to emphasize this yet again.”