Mr Obama is also expected to reiterate¹（重申） America's support for its Nato allies in Europe and keep up pressure on Russia over its role in the crisis.

 

In April, the US sent 150 soldiers into Poland for military exercises amid growing tensions with Moscow.

 

Mr Obama's meetings in Warsaw are part of a European tour which will also take him to Belgium and France.

 

In Belgium, the US leader is expected to urge Western leaders to reaffirm their united position on Ukraine at a G7 meeting of major industrial nations.

 

The summit had been initially² planned in Russia, but Western leaders later decided³ to boycott⁴ it following Moscow's annexation⁵ of Crimea from Ukraine in March.

 

In France, Mr Obama will take part in ceremonies to commemorate⁶ the 70th anniversary of the D-Day landings in Normandy.

 

President Vladimir Putin is also invited, but the White House has already made it clear that the American and Russian leaders will not hold formal bilateral⁷ talks.

 

Washington has repeatedly warned Moscow that it faces new sanctions if it refuses to de-escalate（逐步增强） tensions in eastern Ukraine, where fierce fighting has continued between separatists and Ukrainian government troops. 

 

On Monday, hundreds of rebels attacked a border command centre near the eastern Ukrainian city of Luhansk,

 

The Kremlin denies Western claims that it is supporting the rebels.

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