Russian President Vladimir Putin and Belarusian President Alexander Lukashenko have agreed to deepen bilateral ties amid economic sanctions by Western countries.
The two presidents chaired a meeting in the second largest Russian city of St. Petersburg on Monday.
Russia's presidential office has quoted Putin as saying that it is important for the two nations to closely cooperate in the world, "invariably rendering truly allied assistance to each other in conditions of unprecedented external pressure."
Lukashenko said that both countries will promote their common values.
The two leaders spent three straight days together, attending a memorial event for the victims of World War Two held on Saturday.
Meanwhile, Ukrainian President Volodymyr Zelenskyy referred to the US assistance to his country in an interview with the German public broadcaster ARD released on Sunday.
Asked about what will happen if the US stops its assistance, he said that there will be a deficit of weapons and finances in Ukraine, and the sanctions policy towards Russia may begin to crumble.
The United States, which is Ukraine's biggest backer, faces a stalemate in Congress over an emergency spending bill to continue military assistance to Ukraine.
Former President Donald Trump, who is the frontrunner in the Republican presidential nomination race, has expressed disapproval of the US support to Kyiv.
Zelenskyy stressed the importance of the US assistance, noting that Europe alone cannot support Ukraine.