Premiers from the world's leading economic powers will renew pressure on Russia to act over the crisis in Ukraine at a summit in Brussels.
Leaders of the G7 group of economic powers will also try to thrash out the outline of an agreement over tackling the threat from terror posed by the Syrian conflict.
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Temperatures will reach around 28 Celsius (82F) at their highest.
A minute's silence will be observed at 11am on Thursday in remembrance of those who lost their lives in the Manchester Arena attack.
New research has found those who consumed two cups had a 35% reduced risk, and for those who drank five cups, the risk halved.