Moscow (CNN) -- Police in the Russian city of St. Petersburg have arrested two gay rights activists for breaching a new law that bans the "promotion of homosexuality" to minors, state news agency RIA Novosti reported Saturday.
The two men were detained on Thursday after picketing against the law, which came into effect on March, the news agency said.
St. Petersburg is one of four regions in Russia to impose fines for the dissemination of "gay propaganda" to minors, according to the state-owned Itar-Tass news agency. The others are the Ryazan, Arkhangelsk and Kostroma regions.
Gay rights activists in St. Petersburg have challenged the law in court, arguing that any mention of homosexuality can now be considered an offense under the bill, RIA Novosti said.
The U.S. State Department raised concerns over the legislation before it was passed by St. Petersburg city authorities.
Spokeswoman Victoria Nuland said the law "would severely restrict freedoms of expression and assembly for lesbian, gay, bisexual and transgender (LGBT) individuals, and indeed all Russians. As Secretary (of State Hillary) Clinton has said, gay rights are human rights, and human rights are gay rights.
"We have called on Russian officials to safeguard these freedoms, and to foster an environment which promotes respect for the rights of all citizens."
The United States is liaising with the European Union, as well as Russian officials, on the issue, Nuland said in February.
The European Parliament has also voiced concern over regional legislation in Russia that restricts gay rights.
CNN's Zarifmo Aslamshoyeva and Laura Smith-Spark contributed to this report.