Ukrainian President Petro Poroshenko will meet Russia's Vladimir Putin to discuss the crisis in eastern Ukraine. Mr Poroshenko said he would ask for the pro-Russian rebels to be withdrawn from Ukraine, according to the presidential website.
Mr Poroshenko is scheduled to see Mr Putin in the Belarussian capital Minsk on August 26 at a meeting that will also include top leaders of the European Union and of the Russian-led Customs Union.
More top news
Some 66 people have been killed after the plane they were travelling on crashed in southern Iran.
The letter calls for an end to harassment, abuse, and impunity in a world "ripe for change".
Police say that anyone who sees Whitehouse should not approach him, but instead call them on 999 and quote incident 23 of 18 February.