In photos: Opposing groups clash after pro-Trump protests decry president's election loss

Thousands of Donald Trump supporters alleging electoral fraud took part in protests in several U.S. cities.

A person holds a sign during a rally to protest the results of the election, in front of the U.S. Supreme Court, in Washington, U.S., Dec. 12, 2020.

In Washington, D.C., more than 20 people were arrested and four people were stabbed, police said.

A vehicle with Christmas decorations and signs on it is seen near the U.S. Capitol during a rally to protest the results of the election, in Washington, U.S., Dec. 12, 2020.

Supporters of U.S. President Donald Trump take part in a rally to protest the results of the election, in Washington, D.C., Dec. 12, 2020.

Police use pepper spray as they try to keep members of the far-right group Proud Boys away from counterprotesters during a march in response to various pro-Trump rallies held throughout Washington D.C., Dec. 12, 2020.

A member of the far-right group Proud Boys yells at police to let them through as they march on a street near the White House, during a rally to protest the results of the election, in Washington, D.C., Dec. 12, 2020.

Counterdemonstrators march in response to various pro-Trump rallies held throughout Washington, D.C., Dec. 12, 2020.

A supporter of U.S. President Donald Trump fights with counterprotesters during a march in response to various pro-Trump rallies held throughout Washington, D.C., Dec.12, 2020.

A supporter of U.S. President Donald Trump carries a flag near a police line during a rally to protest the results of the election, in Washington, D.C., Dec. 12, 2020.

Police try to stop a woman as she uses pepper spray during a march in response to various pro-Trump rallies held throughout Washington, D.C., Dec. 12, 2020.

Members of the far-right group Proud Boys clash with counterprotesters, in downtown Washington, D.C., Dec. 12, 2020.

Members of the far-right group Proud Boys talk before marching to protest the results of the election, in Washington, D.C., Dec. 12, 2020.

Police officers stand in formation to separate members of the far-right group Proud Boys and counterprotesters, in downtown Washington, D.C., Dec. 12, 2020.

A supporter of U.S. President Donald Trump fights with counterprotesters during a march in response to various pro-Trump rallies held throughout Washington, D.C., Dec. 12, 2020.

Counterprotesters yell and throw objects as police officers pepper spray them during a march in response to various pro-Trump rallies held throughout Washington, D.C., Dec. 12, 2020.

A member of the far-right group Proud Boys carries a bottle of alcohol and a helmet at a march protesting the results of the election, in Washington, D.C., Dec. 12, 2020.

Riot police line up near Black Lives Matter plaza during a march of counterprotesters in response to various pro-Trump rallies held throughout Washington, D.C., Dec. 12, 2020.

Members of the far-right group Proud Boys prepare to march to protest the results of the election, in Washington, D.C., Dec. 12, 2020.

A member of the far-right group Proud Boys is helped after being pepper-sprayed at a march amid protests against the results of the election, in Washington, D.C., Dec. 12, 2020.

A man argues with a group of Proud Boys during a rally to protest the results of the election, in Washington, D.C., Dec. 12, 2020.

Counterdemonstrators face-off with law enforcement amid protests against the results of the presidential election, in Washington, D.C., Dec. 12, 2020.

Supporters of U.S. President Donald Trump wave flags outside the D.C. Mayor's office building during the “Stop the Steal” rally, in Washington, D.C., Dec. 12, 2020.