ISTANBUL (Reuters) - Turkish authorities have detained three men suspected to have been plotting an attack on German diplomatic missions and a German school in Turkey, the private Dogan News Agency reported on Wednesday.

The three, including an Iraqi and a Syrian national, were captured in Istanbul in an operation by counter terror police units, helped by Turkish and German intelligence, Dogan said.

Medical checks on the three had been completed and police were questioning them, the news agency added.

Germany shut its diplomatic missions and schools on Thursday, citing a specific threat, two days before a suicide bombing in Istanbul blamed on Islamic State militants killed four tourists, the fourth such attack this year in Turkey.

President Tayyip Erdogan said on Monday Turkey was facing one of the ‘biggest and bloodiest terrorist waves in its history”. Another suicide attack in January in Istanbul was also blamed on Islamic State while two others in the capital Ankara have been claimed by Kurdish militants.

A manhunt for three other suspected Islamic State militants thought to be planning suicide bomb attacks is also underway, Turkish officials said on Monday.