Senate Homeland Security Chairman Gary Peters (D-Mich.) on Tuesday pressed video-sharing app TikTok for information about its efforts to curb violent extremist content before and after the Jan. 6 riot at the U.S. Capitol, expanding the panel’s probe into how social media may have contributed to the violence.

Peters expressed concern over reports that domestic extremists used the platform to “recruit, organize and communicate” in the days leading up to the riot, and that they “continue to spread their messages through content supporting white supremacists, extremists, and terrorist organizations.”

He called on TikTok to provide the panel with information by Oct. 27 on how it enforced policies against extremist and violent content before and after Jan. 6, whether the company cooperated with federal authorities in those efforts and whether its algorithms amplified any of that content.

In a letter to TikTok CEO Shou Zi Chew, Peters accused the company of taking action against some extremist content only “after continued reports from outside parties,” and said that “TikTok extremist content has been allowed to return and continue operating on its platform.”

Spokespeople for TikTok did not immediately respond to a request for comment.

Last month, as part of an investigation by the Senate committee into the insurrection, Peters sent similar letters pressing Facebook, Twitter and Google-owned YouTube for information regarding their policies and enforcement against extremist content related to Jan. 6. Tuesday’s letter marks an expansion of those efforts and increases scrutiny on TikTok’s alleged role in the events, which has drawn less attention than those of its peers.

The committee confirmed to The Washington Post last week that it also plans to meet with Facebook whistleblower Frances Haugen, who has accused the company of contributing to the Jan. 6 events.

The House select committee investigating the Jan. 6 riot also has pressed Facebook, YouTube, Twitter and TikTok for information about their roles in policing content surrounding the riot.

Peters on Tuesday also sent letters to the Department of Homeland Security and the FBI, calling on them to disclose more details about their efforts to investigate and disrupt domestic terrorism and extremism on social media platforms.

In a letter to DHS Secretary Alejandro Mayorkas, Peters wrote that “concerns still exist over DHS’s actions to combat the proliferation of domestic extremism on social media, and how the Department has prioritized its resources to counteract that threat.”

DHS and the FBI did not immediately respond to requests for comment.