Violence disrupted a rally in the Democratic Republic of Congo’s capital that was organized by opposition groups seeking to pressure President Joseph Kabila into respecting term limits mandated by the country’s constitution.

Opposition leaders including Vital Kamerhe of the Union for the Congolese Nation had addressed supporters in Kinshasa for an hour when the crowd was attacked by a small group of youths armed with sticks, leading to a stampede and retaliations in which people were injured. Speaking in an interview afterwards, Kamerhe declined to speculate on who was responsible for the attack.

A large crowd attended the gathering, at which Bazaba Masudi, secretary-general of the Movement for the Liberation of Congo, and Martin Fayulu, president of the Engagement for Citizenship and Development also spoke. Kamerhe said it was the first time that an opposition group had filled the square, near the capital’s N’djili international airport. The rally was authorized by Kinshasa’s governor on Sept. 11.

The opposition organized the meeting to call on Kabila to step down at the end of his second and constitutionally-mandated final term in November 2016.

“A president is required to protect the constitution and Kabila must do just that,” Kamerhe said during the rally. He later said the opposition would continue to organize meetings and protests, despite the violence.