COLOGNE, Germany — Women’s rights activists, far-right demonstrators and left-wing counter-protesters took to the streets of Cologne on Saturday to voice their opinions in the debate that has followed a string of New Year’s Eve sexual assaults and robberies in the city blamed largely on foreigners. Amid the heightened public pressure, Chancellor Angela Merkel’s party proposed stricter laws regulating asylum-seekers in the country — some 1.1 million of whom arrived last year. Police said four people were taken into custody and the PEGIDA demonstration was shut down early by authorities using water cannons after protesters threw firecrackers and bottles at some of the 1,700 police on hand. The attackers were among about 1,000 men gathered at Cologne’s central train station, some of whom broke off into small groups and surrounded women, groping them and stealing their purses, cell phones and other belongings, according to authorities and witness reports.