U.N. human rights chief Michelle Bachelet on Thursday called on Russian President Vladimir Putin to “halt armed attack against Ukraine.”

Speaking a day after the conflict reached its six-month mark, Bachelet highlighted the situation regarding the Zaporizhzhia nuclear power plant, saying fighting in the area is posing “unthinkable risks” to civilians and the environment.

Russia and Ukraine have blamed each other for attacks near the plant, and the International Atomic Energy Agency has said it is ready to send teams to the site to ensure its safety.

Bachelet also said Thursday that both Russian and Ukrainian forces must respect international humanitarian rights law, while the international community must ensure accountability for violations.

Ukrainian officials said Thursday the death toll from a Russian missile strike on a railway stay in eastern Ukraine rose to 25 after several more bodies were found in the rubble in the town of Chaplyne.

“Russia’s missile strike on a train station full of civilians in Ukraine fits a pattern of atrocities,” U.S. Secretary of State Antony Blinken tweeted. “We will continue, together with partners from around the world, to stand with Ukraine and seek accountability for Russian officials.”

U.S. President Joe Biden on Wednesday praised the “extraordinary courage and dedication to freedom” of the Ukrainian people in fending off Russian fighters, while announcing nearly $3 billion in new military aid.

On Ukraine’s Independence Day, marking 31 years since escaping Soviet rule in 1991, Biden said the day “is not only a celebration of the past, but a resounding affirmation that Ukraine proudly remains — and will remain — a sovereign and independent nation.”

Biden said the new tranche of military assistance was designed to help Ukraine defend itself over the long term, with U.S. officials saying some of the weaponry might not be used for a year or two. The U.S. leader said the package would include air defense systems, artillery systems and munitions, counter-unmanned aerial systems, and radars.

The new aid comes on top of about $10.6 billion in military assistance the U.S. has already sent to Ukraine in the last year and a half.

Biden said he knows that this year’s Independence Day “is bittersweet for many Ukrainians as thousands have been killed or wounded, millions have been displaced from their homes, and so many others have fallen victim to Russian atrocities and attacks.”

He added, “Today and every day, we stand with the Ukrainian people to proclaim that the darkness that drives autocracy is no match for the flame of liberty that lights the souls of free people everywhere.”

Some information for this story came from The Associated Press, Agence France-Presse and Reuters.