At least seven people, including two policemen, have died amid escalating violence in Ukraine.

The clashes, between protestors and police, are the worst for weeks and come as MPs are due to debate changes to the constitution.

Ukraine’s Interior Ministry said two policemen and five civilians had been killed in clashes on Tuesday.

The clashes broke out near parliament. Protesters torched vehicles and hurled stones. Security forces – including the Berkut riot police – replied by firing rubber bullets as well as stun and smoke grenades from trucks and from the tops of buildings.

Dozens of people are reported injured, on both sides. As well as the deaths, opposition medical sources said at least 150 activists had been hurt, 30 of them seriously.

Demonstrators had been trying to march on parliament ahead of a crucial debate but they were blocked from approaching the building by security forces.

Activists stormed, set fire to and briefly occupied a building belonging to President Viktor Yanukovych’s political party amid scenes described as “open warfare”.

It is three months since protests first broke out over Yanukovych’s rejection of an EU trade deal in favour of closer ties with Russia. They have since broadened into a revolt against perceived sleaze and corruption in his leadership.

The opposition are pushing for a vote on constitutional change to reduce his powers but as moves in parliament were thwarted, frustration spilled out onto the streets.

The fresh violence is the result of Western policies encouraging a flare-up, Russia’s Foreign Ministry said in a statement.

Opposition leaders have vowed that the protest movement will continue.