ISTANBUL -- Turkey's President Recep Erdogan says it's a "scandal" that a U.S. court has decided to indict 19 people, among them 15 Turkish security officials.

Erdogan's comment follows the indictments of people accused of attacking peaceful demonstrators gathered outside the Turkish ambassador's Washington home during a visit by Erdogan on May 16.

Erdogan said Friday that the security officials were protecting him from members of an outlawed Kurdish militant group after U.S. police failed to. One of those indicted is the head of Erdogan's security operation.

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He called the indictment "a clear and scandalous expression of how justice works in America" and said he would raise the issue with President Trump during a visit to New York this month.

The case threatens to further complicate already tense relations between the two NATO allies. Ankara strongly opposes the U.S. decision to arm Syrian Kurdish rebels fighting the Islamic State group in Syria. Turkey views the Syrian Kurds as an extension of its own outlawed Turkish Kurdish movement and opposes any moves that could lead to the formation of an independent Kurdish state.