A woman reacts as she talks to journalists following a Russian missile strike, as Russia's attack on Ukraine continues, in Kramatorsk, Donetsk region, Ukraine on October 4, 2022. [Reuters]

Ukrainian President Volodymyr Zelenskyy signed a decree Tuesday declaring that negotiating with Russian President Vladimir Putin has become “impossible” following Putin’s attempt to annex four Ukrainian regions.

Kremlin spokesman Dmitry Peskov told reporters that Russia would wait until Zelenskyy changes his mind or until a new president takes office in Ukraine.

Meanwhile, the White House said U.S. President Joe Biden assured Zelenskyy in a phone call that “the United States will never recognize Russia’s purported annexation of Ukrainian territory.”

Biden also said the U.S. was ready “to impose severe costs on any individual, entity, or country” that supported Russia’s annexation claim.

In addition, Biden told the Ukrainian leader the U.S. was sending the Kyiv government another $625 million in armaments to help it fend off Russia’s seven-month invasion, bringing total arms aid to more than $17.5 billion since January 2021, when Biden took office.

Earlier Tuesday, the upper house of Russia’s parliament voted to make the four Ukrainian regions part of Russia, pushing forward with a process that has been condemned by Ukraine and its Western allies and was described by U.N. Secretary-General Antonio Guterres as a "dangerous escalation" that has "no legal value."

Russia’s lower house already gave its approval after Russia organized what it claimed to be referendums in four regions of Ukraine occupied by Russian troops.

Ukraine said the voting was held under coercive conditions and did not represent the will of the people in Donetsk, Luhansk, Zaporizhzhia and Kherson.

Guterres said last week that "annexation of a state’s territory by another state resulting from the threat or use of force is a violation of the principles of the U.N. Charter and international law."

Ukrainians forces keep gaining

While Russia pushes ahead with its annexation claims, Ukrainian forces have made gains in a counteroffensive in Russia-held areas.

Russia-installed officials in Kherson said Ukraine’s military had recaptured some settlements, while the Russian Defense Ministry acknowledged that "with superior tank units," Ukraine had "managed to penetrate into the depths of our defense."

Ukrainian President Volodymyr Zelenskyy said in his nightly address Monday that Ukraine’s military was moving ahead with its advances. Without providing details, he said the army had seized back towns in several areas.

"New population centers have been liberated in several regions. Heavy fighting is going on on several sectors of the front," he said.

Zelenskyy said Sunday that his forces in Kherson had liberated the settlements of Arkhanhelske and Myroliubivka.

Still, a Russian defense spokesman said Moscow’s troops "have occupied a pre-prepared defensive line and continue to inflict massive fire damage" on Kyiv’s forces.

A senior U.S. military official said Monday that the United States sees heavy fighting continuing as Russian forces try to push west, "but no significant shifts on the ground have occurred as Ukrainian forces continue to hold the line."