Ukraine's President Petro Poroshenko (L) and US President Donald Trump meet for atalks on the sidelines of the 72nd session of United Nations (UN) General Assembly.

Ukraine has secured U.S. assurances that President Donald Trump will not betray its interests when he holds his first bilateral summit meeting with Russian leader Vladimir Putin in Helsinki on July 16.

But Trump is known for his spontaneous and sometimes erratic style of doing diplomacy, and Kiev fears that behind closed doors he may prove susceptible to Putin’s efforts to win U.S. acceptance of Russia’s 2014 annexation of Crimea from Ukraine.