MOSCOW — Allies of jailed Russian opposition leader Alexei Navalny, who faces years in prison, called for new protests next weekend to demand his release, following a wave of demonstrations that turned out tens of thousands across the country in a defiant challenge to President Vladimir Putin. Mass rallies took place Saturday in over 100 cities in what observers said was the largest outpouring of anger in years, and Navalny’s supporters urged protesters to keep up the pressure. Navalny strategist Leonid Volkov tweeted Monday for more demonstrations on Jan. 31 in “all Russian cities. … For Navalny’s freedom. For our freedom. For justice.” During Saturday’s protests, over 3,700 people were detained, according to OVD-Info, a human rights group that monitors political arrests. The group said the number was a record in its nine years of work. More than 1,400 detentions occurred in Moscow alone — also a record, according to Russian media. Some of those detained were released...