Thailand has started voting on in an election called by Prime Minister Yingluck Shinawatra in December in an attempt to defuse protests aimed at overthrowing her.
However, the protesters are still out on the streets and say they may disrupt voting. The main opposition Democrat Party is boycotting the election.
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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.