Turkish authorities have launched an investigation into restoration work carried out on a historic tower near Istanbul after social media users derided the construction, likening it to the cartoon character SpongeBob SquarePants.

Adem Avgin, an official in charge of projects at the mayor's office in the Black Sea coastal town of Sile, told the state-run Anadolu Agency on Thursday that an inspection was being carried out to determine whether restoration of the Byzantine-era tower remained "true" to the original project.

Hurriyet newspaper and other media printed photos of a modern-looking, square-shaped construction with windows and slits that resemble eyes and eyebrows, juxtaposed to SpongeBob images.

Avgin defended the restoration work, saying the tower was on the verge of collapsing.