Reyhanli, Turkey (CNN) Mazin Yusif, 13, sauntered around the hospital with the confidence of a regular, taking us from room to room, introducing the people in each ward.

He arrived here at the Reyhanli State Hospital 24 hours ago, one of around 30 Syrians rushed to this southern Turkish town near the Syrian border after what appears to have been a chemical attack by Syrian warplanes on rebel-held Khan Shaikhoun in Idlib province.

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The attack killed at least 70 people, including children, one of the deadliest since the Syrian war began six years ago.

The World Health Organization said victims bore the signs of exposure to nerve agents. Syrian President Bashar al-Assad's military categorically denied using chemical weapons and blamed "terrorist" groups for the carnage.

Mazin wore new clothing, crisp blue jeans and a red, white and blue jacket -- he'd lost his own in the attack. His eyes were bloodshot, his voice was hoarse.

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