As heavy fighting continues in the eastern regions of Ukraine, President Volodymyr Zelenskyy has said that the situation on the front is very difficult but remained defiant.

The Ukrainian defense ministry also noted on social media on Saturday that Russians are intensifying their war effort in the Ukraine's eastern regions of Donetsk and Kharkiv.

Zelenskyy talked of the difficult situation in Bakhmut, a stronghold of Ukraine in Donetsk, in his video speech on Saturday.

He said that "the occupier throws in more and more of its forces to break our defenses." He stressed the importance of resilience among Ukrainian soldiers.

Zelenskyy touched upon Challenger 2 tanks that Britain promised to provide, saying training has already begun in the UK to teach Ukrainian soldiers how to use them. He noted that this will be significant.

The United States on Friday announced more military aid to Ukraine, including long range rockets.

Former Russian President and current Deputy Chairman of Russia's Security Council Dmitry Medvedev reacted to the news by mentioning the potential use of nuclear weapons.

He said in a written interview with a Russian reporter on Saturday that Russia can use all kinds of weapons in accordance with the "basic principles of nuclear deterrence" and that the response will be fast and severe.

Medvedev is known for using hardline language on western military assistance to Ukraine.