The U.S. is concerned by the detention of human rights activists, who gathered for an unsanctioned rally in downtown Moscow on Sunday, a spokesman for the Department of State said.

"The United States is concerned by reports that authorities in Moscow on January 31 once again broke up a peaceful demonstration by Russian citizens," Gordon Duguid, an acting deputy department spokesman, said in a statement.

Moscow police detained some 100 people, including leader of the opposition movement The Other Russia, Eduard Limonov, former Russian deputy prime minister Boris Nemtsov and head of the Memorial human rights group Oleg Orlov, after they gathered along with some other 200 protesters on Triumphalnaya Square.

"The detention of at least 100 protestors, including prominent human rights defenders and opposition political leaders, together with reports of mistreatment against some of the demonstrators, constitutes another blow against freedom of speech and assembly, which are universal and fundamental rights that deserve to be protected and promoted," he added.

The protesters said they gathered to show that the authorities are violating the Russian Constitution, which grants the right to assemble peacefully.

In a similar crackdown on protesters on the Triumfalnaya Square just hours before the New Year Moscow police arrested about 50 people, including 82-year-old head of the Moscow Helsinki group, Lyudmila Alexeyeva, prompting criticism from the United States and European human rights organizations.

WASHINGTON, February 2 (RIA Novosti)