 -- The U.S. detained and released two members of the Turkish president's delegation after they were involved in an attack on peaceful protesters outside the Turkish embassy Tuesday.

The diplomatic incident has sparked outrage in Washington and even prompted the State Department to summon the Turkish ambassador.

Violence erupted when Turkish security officials and counter-protesters clashed with demonstrators near the ambassador’s residence, where President Recep Tayyip Erdogan stayed after meetings with President Trump at the White House. The incident left 11 people injured, nine of whom were hospitalized. Washington D.C. police, fire fighters, and EMS all responded, shutting down traffic in the area..

The Turkish security officials were briefly detained at the site of the protest by U.S. law enforcement for their role in the altercation. But because of their diplomatic immunity, they were released on the scene.

"Customary international law affords heads of state and members of their entourage with inviolability from arrest and detention," a State Department official told ABC News. "The United States recognizes this inviolability, which provides reciprocal protection for the United States abroad."

Still, the State Department said it was expressing "concern" to Turkey over the incident "in the strongest possible terms." The U.S. response included summoning the Turkish ambassador to the State Department Wednesday, where he met with Under Secretary of State Tom Shannon, the acting Deputy Secretary.

Two men were also arrested by D.C.'s Metropolitan Police Department on the scene -- Jalal Kheirabaoi of Fairfax, VA, and Ayten Necmi of Woodside, NY, according to police reports. It is unclear if they worked for the embassy or were members of the counter-protest.

Members of Congress from both parties have expressed their outrage over the incident. Senator John McCain, R-AZ, and Senator Claire McCaskill, D-MO, both called for the expulsion of Turkey's ambassador.

"Obviously he was in charge of the group of thugs that violated American law and beat up people," McCain told ABC News. "It's disgraceful and shouldn't be happening in the United States of America."

I agree with @SenJohnMcCain.Unacceptable. They were assaulting these people on US soil.Turkish Ambassador should be kicked out of country. https://t.co/PtCS1qG51K

A State Department official declined to comment on the idea of expelling the ambassador.

McCain also sent a letter to Erdogan along with his Democratic colleague, Sen. Dianne Feinstein of California, calling on him to hold his staffers accountable.

"Your staff’s blatant violation of these rights on American soil is an affront to those freedoms, and reflects poorly on your government," they wrote.

The White House hasn’t commented on the altercation, but President Trump has been criticized for his positive comments on foreign leaders, like Erdogan, who have been criticized for their records on political freedom and human rights.

In their Oval Office meetings Tuesday, Trump did not mention Erdogan's increasingly tight grip on power in Turkey or allegations of irregular elections under his leadership.