The three males -- two boys aged 17 from north-west London and a man aged 19 -- were detained in Istanbul, and were feared to be on their way to join IS extremists.
They were reported missing on Friday and were detained after UK counter-terrorism officers alerted Turkish officials, the Metropolitan Police said.
Their families have been "kept informed of developments", the Met said.
Scotland Yard said counter-terrorism officers had initially been made aware that the two 17-year-old boys had gone missing and were believed to be traveling to Syria.
"Officers alerted the Turkish authorities who were able to intercept all three males, preventing travel to Syria. They remain in detention in Turkey," a Met spokesperson added.
The latest arrests come after Shamima Begum, Amira Abase, both 15, and Kadiza Sultana, 16 -- schoolgirls from London -- took flights to Istanbul last month, from where it is feared they traveled to Syria.
Their disappearance led to criticisms from Turkey's deputy prime minister, who said officials in the country had not been given enough warning about their disappearance.
A large number of Britons have traveled to Turkey, using the country as a crossing point to eventually enter Syria to join IS militants, who control large swaths of territory in Syria and Iraq.
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