U.S. authorities are trying to seize an ancient gold ring allegedly looted by Islamic State militants that was sold for around $250,000 in Turkey and then confiscated by Turkish police, according to court documents filed Wednesday.

In a related action, U.S. officials identified several new ancient objects allegedly looted by Islamic State in Syria and have filed an amended complaint to seize the items, which include a gold brooch and necklace worth tens of thousands of dollars. The location of those items is unclear.

The...