Large numbers of Russians rushed to book one-way tickets out of the country while they still could Wednesday after Russian President Vladimir Putin announced a partial mobilization of military reservists for the special military operation in Ukraine. Flights filled up quickly and the prices of tickets for remaining connections sky-rocketed, apparently driven by fears that Russia's borders could soon close or of a broader call-up that might send many Russian men of fighting age to the frontline. Tickets for the Moscow-Belgrade flights operated by Air Serbia, the only European carrier besides Turkish Airlines to maintain flights to Russia despite a European Union flight embargo, sold out for the next several days. Russians don't need visas to enter Serbia, which is the only European country which has not joined Western sanctions against Russia. Putin's decree stipulates that the amount of people called to active duty will be determined by the Defense Ministry. Defense Minister Sergei Shoigu said in a televised interview that 300,000 reservists with relevant combat and service experience initially would be mobilized. Meanwhile in Russia, police in riot gear packed protesters into buses on Wednesday as St. Petersburg joined other Russian cities to rally against the military mobilization. Nearly 1,200 Russians were arrested in protests in cities including Moscow and St. Petersburg, according to the independent Russian human rights group OVD-Info.