By Pavel Polityuk and Natalia Zinets
KIEV (Reuters) - At least 50,000 opponents of Ukrainian President Viktor Yanukovich rallied in a central Kiev square on Sunday, reviving an anti-government protest movement after a Christmas and New Year lull.
The mass rally in Independence Square was a continuation of street protests that erupted in November after Yanukovich decided to abandon a free trade agreement with the European Union in favor of closer cooperation with Russia.
The demonstration came a day after baton-wielding riot police tried to disperse protesters outside a Kiev courthouse, sparking clashes in which at least 10 people were injured.
"What are the next steps? We will fight, ... protest peacefully," Vitaly Klitschko, an opposition leader and former world heavyweight boxing champion, told a crowd waving the blue-and-yellow national flags of Ukraine.
He accused the authorities of using the police to silence protests, and repeated the opposition's call for early presidential elections, which are not due until 2015.
Another opposition leader, Arseny Yatsenyuk, called on the West to impose sanctions against senior state officials, including Interior Minister Vitaly Zakharchenko, who, he said, had violated Ukraine's constitution by authorizing the use of force against the protesters.
On January7, the U.S. Senate passed a non-binding resolution urging the U.S. president and Congress to consider applying sanctions including visa bans and asset freezes against any officials who ordered or carried out violence against protesters.
The U.S. Senate Committee on Foreign Relations is due to hold a hearing on Ukraine on January 15.
In November, Yanukovich's government walked away at the last minute from a deal tying Ukraine more closely to the European Union and opted for closer ties with Kiev's Soviet-era overlord, Moscow.
The decision prompted street demonstrations opposing the decision, and the movement quickly developed into an all-out protest against Yanukovich and his government.
The protest rallies attracted as many as 800,000 people at their height but the movement quietened over New Year and the Ukrainian Orthodox Christmas, which was celebrated on January7.
(Additional reporting by Susan Cornwell in Washington, writing by Gabriela Baczynska; Editing by Kevin Liffey)