King Charles told President Recep Tayyip Erdogan that his "thoughts and special prayers" are with all those affected by the earthquake in Turkey.
In a message shared on Tuesday, the monarch wrote: "My wife and I have been most shocked and profoundly saddened by the news of the devastating earthquakes in South East Turkiye (Turkey).
"I can only begin to imagine the scale of suffering and loss as a result of these dreadful tragedies and I particularly wanted to convey our deepest and most heartfelt sympathy to the families of all those who have lost their loved ones.
"Our thoughts and special prayers are with everyone who has been affected by this appalling natural disaster, whether through injury or the destruction of their property, and also with the emergency services and those assisting in the rescue efforts."
President Recep Tayyip Erdogan speaks to the press following the earthquake
According to the BBC, more than 6,300 people have been killed in southern Turkey and northern Syria following a 7.8-magnitude quake in the early hours of Monday, and a 7.5-magnitude tremor hours later.
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As rescue efforts are carried out in the two countries, there are fears that the death toll could continue to rise.
The King's message comes hours after he hosted an investiture ceremony at Windsor Castle, where he handed out honours to fashion designer, Stella McCartney, and 90s rock star Skin, lead vocalist of Brit-rock band Skunk Anansie.
Monarchs from around the world have been united in their grief following the earthquakes.
Among those to share messages of condolences and support were King Abdullah and Queen Rania of Jordan, King Willem-Alexander and Queen Maxima of The Netherlands, Queen Margrethe of Denmark, King Carl XVI Gustaf of Sweden and King Harald of Norway.
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