KIEV, Ukraine — Ukraine's security agency is warning of a heightened risk of terrorism amid nearly three months of anti-government protests.

The agency said in a statement Sunday that it was putting its counter-terrorism units on alert, after receiving a large number of bomb threats across the country at airports, train stations, pipelines and other locations.

In what was seen as a warning to the opposition, the agency also said that it views the seizures of government buildings by protesters as manifestations of terrorism.

Some 30,000 activists turned out for a rally on Kiev's Independence Square on Sunday, the day the protests usually draw the largest crowds.

The protests started after President Viktor Yanukovych ditched a key treaty with the European Union in favor of a bailout loan from Russia.