MOSCOW — Thousands marched in a pro-invasion rally in downtown Moscow one day after Russia's parliament gave President Vladimir Putin a green light to use military force in Ukraine.

At least 10,000 people bearing Russian flags marched freely through Moscow on Sunday, while dozens of people demonstrating on Red Square against an invasion of Ukraine were quickly detained by Russian riot police.

The Associated Press witnessed over 50 detentions and spotted at least five police vans, which carry between 15 and 20 protesters, driving away from the square.

Many Russians believe the country should maintain strong ties with Ukraine's predominantly Russian-speaking eastern and southern regions. But Russia's state-controlled TV stations have ratcheted up that rhetoric after months of pro-democracy protests in Ukraine forced its Russia-leaning President Viktor Yanukovych to flee Ukraine.