Russian investigators are questioning two top protest leaders about their roles in anti-government demonstrations that led to clashes with police.

Popular opposition blogger Alexei Navalny and coordinator of the Left-Wing Front movement Sergei Udaltsov were arrested late Tuesday with dozens of other activists participating in a protest near the Kremlin.

The Russian Investigations Committee says the two men were being questioned Thursday as part of a probe into the demonstration.

They were each sentenced on Wednesday to 15 days in jail for their role in the demonstrations.

Moscow police also detained hundreds of protesters during a rally Sunday, one of the latest in a series of demonstrations against Russia's elections and Vladimir Putin's return to the presidency.

Mr. Putin was elected to a third presidential term in March with 64 percent of the vote. He served as president from 2000 to 2008, but term limits prevented him from running for a third consecutive term. He then became prime minister under former president Dmitry Medvedev.

A constitutional amendment has extended the president's time in office to two consecutive six-year terms, meaning Mr. Putin could stay in power until 2024 — an outlook many Russians find unsettling.

Meanwhile, Mr. Putin says he will skip this month's planned visit to the United States for a Group of Eight industrial nations meeting outside Washington.

The Kremlin says the Russian leader told U.S. President Barack Obama in a telephone call Wednesday that he has a responsibility to remain in Moscow to finalize Cabinet appointments to his new government.

Former president Medvedev, who now is the new prime minister, will attend the G8 summit in Mr. Putin's place. The White House says Mr. Putin agreed to meet with President Obama during the G20 summit next month in Mexico.