MOSCOW, Aug. 10 (Xinhua) -- Washington and Moscow are caught in a fresh round of tit-for-tat over recent U.S.-imposed sanctions, which threatens to dim the silver lining in bilateral ties.

The U.S. State Department Wednesday vowed to take punitive measures against Russia over an alleged nerve agent attack on ex-Russian spy Sergei Skripal and his daughter Yulia in the British city of Salisbury earlier in March.

Meanwhile, Moscow has vehemently denied any involvement in the case and demanded direct participation in the investigation.

Maria Zakharova, spokesperson for the Russian Foreign Ministry said that the U.S. restrictions will possibly comprise of a ban on foreign assistance and the sale of military and dual-use items to Russia, as well as renunciation of providing state loans and other financial aid.

The new sanction triggered a furious reaction from Moscow as Kremlin vowed retaliation against the "unfriendly and unacceptable" move "inconsistent with the constructive atmosphere created after the recent Putin-Trump meeting" in Helsinki, in which hope of thawing ties flickered.

Vladimir Vasilyev, chief research fellow at the Institute of the United States and Canada warned that the recent sanctions mean that the two countries are "slipping into an economic war" and bilateral ties are reaching "a point of no return."

"There will be no positive change in Moscow-Washington relations until the end of the presidential term of Donald Trump", the expert predicted.

Yevgeny Minchenko, a Russian political scientist pointed out that the recent hard-line stance by the Trump administration is part of an effort to demonstrate that "the solidarity within the North Atlantic Treaty Organization is not questioned" and that they are "tougher towards Russia than the Obama administration."

Nile Gardiner of the Washington-based think tank Heritage Foundation echoed the idea, saying that U.S. policy toward Russia is "strengthening rather than weakening" following the Helsinki Summit and such a hardline stance is "a further deterioration of U.S.-Russian relations."

The recent action by Washington is the latest salvo in a series of tit-for-tat spats between the rival powers in March which involved slapping sanctions, the closing of consulates and the expulsion of diplomats.

The ongoing retaliatory measures may nullify the outcomes of the Helsinki Summit, complicating bilateral relations and driving further the vicious circle of hostilities, U.S. experts said.

Russian stocks took an immediate tumble on Thursday in wake of the new sanctions, with the ruble traded around 66 per U.S. dollar, marking the lowest level since 2016.