As the Natural History Museum of America has doggedly refused to return back some 2,500 fossils it had borrowed from Iran in late 1970s, a paleontologist center in northwest of Iran has formed a coalition to sue the American museum in the Hague.

Overseeing one of the world’s most fossil-rich areas, Maraghe’s paleontologist center has a vast collection of fossils, some dating back to the prehistoric eras.

“Maraghe’s paleontologist center, along with Iranian Environment Agency and Natural History Museum, has filed a lawsuit in the Hague against the American museum. We expect that would compel them to return the borrowed properties,” said Nader Ibrahimi, deputy of Iran’s Natural History Museum.

Prior to the 1979 Islamic Revolution over 2,500 fossils were lent to the Natural History Museum of America for academic purposes and both sides agreed that the collection must be returned to its owner after U.S. researchers’ studies. After the revolution, the American side renegade on its promise. Now Iran has decided to take the case to an international court.