MOSCOW—Police detained more than 1,000 people across Russia on Saturday and broke up rallies around the country as protesters defied bitter cold and a ban by authorities to demand the release of jailed Kremlin critic Alexei Navalny. Navalny had called on his supporters to protest after being arrested last weekend as he returned to Moscow for the first time since being poisoned with a military-grade nerve agent in August. Navalny had been treated in Germany. The authorities had warned people to stay away from Saturday’s protests, saying they risked catching COVID-19 as well as prosecution and possible jail time for attending an unauthorised event. But protesters defied the ban and bitter cold, and turned out in force. In central Moscow, where Reuters reporters estimated at least 40,000 people had gathered in one of the biggest unauthorised rallies for years, police were seen roughly detaining people, bundling them into nearby vans. …