Reverberations from the Ukraine war widened on Wednesday, jolting energy markets and spilling across borders, as Russia responded to the West¡¯s escalating arms shipments and economic penalties by halting gas supplies to two European nations and threatening further unspecified retaliation.

The European Union¡¯s top official described as ¡°blackmail¡± the announcement that Russia was suspending shipments of natural gas to Poland and Bulgaria. Though the immediate effect was likely to be limited, the cutoff was the Kremlin¡¯s toughest retaliation yet against a U.S.-led alliance that President Vladimir Putin has accused of waging a proxy war aimed at weakening Russia.

Even as news of a U.S.-Russia prisoner exchange offered a glimmer of hope for diplomatic engagement, Putin warned that he would order more ¡°counterstrikes¡± against any adversaries that ¡°create threats of a strategic nature unacceptable to Russia.¡±