Negotiators from Russia and Ukraine have arrived in Istanbul, Turkey, to hold a fourth round of face-to-face ceasefire talks on Tuesday.

Ukrainian Foreign Minister Dmytro Kuleba said on local TV on Monday that Ukrainian negotiators aim to at least resolve humanitarian issues. He said their main goal is to reach a ceasefire agreement and that they will not trade people, land or sovereignty.

Russian Security Council Secretary Nikolai Patrushev, a close aide to President Vladimir Putin, said on Monday that the military operation is not aimed at seeking a change of government in Ukraine. He said it's to protect people from genocide and to demilitarize and "denazify" Ukraine.

His remarks are believed to be a sign that Moscow will continue ceasefire negotiations with the Ukrainian government under President Volodymyr Zelenskyy, as it faces unexpected difficulties in the war.

The Russian military has indicated it will step up operations in the east of Ukraine and is intensifying its offense to capture the key port city of Mariupol.

A senior US Department of Defense official said on Monday that Mariupol is surrounded by Russian forces and is under intense pressure, while Ukrainian troops have recaptured a town in the northeast of the country.