A spokesman for the Investigative Committee said that Udaltsov denied the accusations during questioning on October 26.
Udaltsov had obeyed a summons to appear at the Investigative Committee for questioning. Arriving at the Investigative Committee earlier on October 26, he denied any wrongdoing.
Vladimir Markin, the spokesman for the Investigative Committee, said Udaltsov had not been detained but remained banned from leaving Moscow.
"I am innocent. I'm going in with my head up high," Udaltsov said. "And if I am arrested today, I hope society will not remain silent and there will be mass protests. I will be fine, I hope everything will be all right, and Russia will be free."
Last week, investigators opened a criminal probe against Udaltsov, his assistant Konstantin Lebedev, and Leonid Razvozzhayev, an assistant to an opposition State Duma deputy.
The investigation was launched after a pro-Kremlin TV channel aired a report that portrayed them plotting riots.
Razvozzhayev Says Abducted
On October 25, Razvozzhayev retracted a confession he allegedly signed in custody, saying he had written the statement under pressure.
Markin, the spokesman for the Investigative Committee, said investigators had enough evidence in the inquiry even without Razvozzhayev's statement.
Investigators say he turned himself in to authorities and confessed on October 22 to plotting unrest with funding from a Georgian lawmaker.
But Razvozzhayev says he was abducted in Ukraine, "tortured," and then brought back to Russia against his will.
The United Nations refugee agency said it was "deeply concerned" after Razvozzhayev's unexpectedly disappeared in Kyiv while meeting with rights lawyers.
Joseph Kruzich, the press attache of the U.S. Embassy in Moscow, said on October 25 that Washington had officially expressed concern to Russian officials over Razvozzhayev's case.
Moscow city officials, meanwhile, warned against opposition plans to hold unauthorized protests on October 27 against the detention of opposition campaigners.
An activist told reporters has said the opposition plans to hold one-person pickets along the road between the Federal Security Service (FSB) headquarters at Lubyanka Square and the Investigative Committee's offices in Lefortovo.
Sergei Parkhomenko said the opposition was also calling on its supporters to "peacefully walk" along the stretch of road between Lubyanka and Lefortovo.