Anti-government protesters filled the streets of Venezuela’s capital and other major cities in a show of force against Presidential Nicolas Maduro, whose allies enraged the opposition by blocking a recall referendum against the socialist leader.

Tens of thousands of demonstrators shut down Caracas’ main highway on Wednesday, many chanting “Democracy yes! Dictatorship no!” And police clashed with protesters in other cities in what opposition leaders called “the takeover of Venezuela.”

Nationwide at least 140 people were detained by police, according to the Foro Penal human rights group. A police officer was shot and killed, and two others injured, under unclear circumstances in central Miranda state.

“Maduro has shown how scared he is that the people will express themselves,” opposition leader Henrique Capriles said.