Hollywood star Robert De Niro has called for doing "something" regarding the killing of Saudi journalist Jamal Khashoggi.

"I am upset about what happened to Khashoggi," De Niro told reporters on the sidelines of the Morocco-based 17th Marrakech International Film Festival.

"That was not good, unacceptable, and something has to be done about it," he said.

Khashoggi, a Saudi journalist and columnist for The Washington Post, went missing after entering the Saudi Consulate in Istanbul in early October.

After initially saying he had left the consulate alive, Saudi Arabia admitted weeks later that he was killed there, blaming his death on a group of rogue Saudi operatives.

On Wednesday, a group of U.S. senators defied the White House and introduced a resolution that would hold Saudi Crown Prince Mohammed bin Salman accountable for the journalist's murder.

Earlier, a Turkish court issued arrest warrants for former Saudi Deputy Foreign Intelligence Chief Gen. Ahmed Asiri and Royal Court Adviser Saud Al-Qahtani over their roles in the murder of Khashoggi.

Saudi authorities launched an investigation against 21 people including Asiri and al-Qahtani over the murder, detaining some of the suspects and seeking death penalty for five.

Asiri and al-Qahtani were sacked from their positions, according to a statement released on Oct. 20.

Turkey has been seeking the extradition of 18 suspects, including 15 members of the assassination squad.

Turkish officials have repeatedly offered for the trial against the murder to be held in Turkey, where the crime was committed. Saudi authorities have denied Turkey's requests and said the suspects will be tried in the kingdom.

With the court's decision, Turkey could now issue an international arrest warrant for the suspects to be detained anywhere in the world.