The United States said Tuesday that it firmly supports Lithuania and its NATO commitments to protect member states after Russia began threatening the Baltic nation over transit restrictions.

State Department spokesman Ned Price said.

"We stand by our NATO allies and we stand by Lithuania," Ned Price was quoted by AFP news agency as saying.

"In particular, our commitment to the fifth article of NATO - saying that an attack on one would mean an attack on all - that commitment on the part of the United States is unwavering," he said.

Price said the United States welcomed the "unprecedented economic measures" taken by Lithuania and others against Russia over its invasion of Ukraine.

Asked about Russia's statements, Price said we are not going to speculate on Russian arms rattling or Russian praise and "don't even want to give them extra airtime."

Lithuania announced restrictions on rail transit of EU-sanctioned goods to the Kaliningrad region, an isolated Russian enclave between Lithuania and Poland.

Russia warned that it would definitely respond to the "hostile actions".