Lefteris Pitarakis, Associated Press
A bird flies past a mosque's minaret in the historic Sultanahmet district in Istanbul, near the site of Tuesday's explosion, Friday, Jan. 15, 2016. A suicide bomber detonated a bomb in the heart of Istanbul's historic district on Tuesday morning, killing a number of German tourists and wounding over a dozen others, in the latest in a string of attacks by the Islamic extremists targeting westerners.

ANKARA, Turkey — Turkey's state-run news agency says 15 academics who were detained for having signed a declaration denouncing military operations against Kurdish rebels, have been released after questioning.

The scholars were among more than 1,000 academics who endorsed the declaration this week, triggering ire from President Recep Tayyip Erdogan and prompting prosecutors to launch probes into the signatories over possible "terrorist propaganda" charges.

The 15 who were released after questioning Friday are lecturers at Kocaeli University in northwest Turkey. Three other academics from Uludag University are still in custody. Authorities meanwhile detained one other academic, the Anadolu Agency reported.