Washington was worried about Tokyo's recent talks with Moscow on a World War II peace treaty, pointing out to its East Asian ally that it should honor Western sanctions against Russia.
"Broadly speaking, it's not time for business as usual with Russia," US State Department spokesperson John Kirby said during a briefing on Thursday.
Kirby warned Japan that it should proceed cautiously when dealing with Russia.
On September 21, following a meeting with Japanese Foreign Minister Fumio Kishida, Russian Foreign Minister Sergei Lavrov stressed that cooperation between Japan and Russia is in the interest of both Tokyo and Moscow and it shouldn't depend on external factors.
Russia's relations with Japan have deteriorated amid the Ukrainian crisis. Japan joined many Western countries and their allies in imposing sanctions against Moscow for its alleged participation in the conflict in Ukraine's southeast.
Russia and Japan have also seen a spike in tensions over the Kuril Islands in the Sea of Okhotsk. All of the Kurils have been administered by Russia since the end of World War II, but the Japanese government still lays claim to Iturup and three other islands.
