Nato Secretary-General Jens Stoltenberg says Russia's violation of Turkish airspace over the weekend "does not look like an accident".
Islamic State claims attacks in the Yemeni city of Aden - including one on a hotel used by the prime minister - that killed 15 Gulf and Yemeni troops.
The EU is offering new incentives to Turkey - including financial aid and easing of visa restrictions - for help to solve the migrant crisis.
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