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Hundreds of hard-line protesters opposed to Ireland's ongoing austerity program have snarled rush-hour Dublin with a surprise seizure of a key bridge.

Police say several protesters have received medical treatment after being pepper sprayed outside the entrance of Ireland's Parliament building.

The protesters had tried to push through steel barricades erected to protect politicians arriving for Wednesday afternoon's reopening of Parliament following a two-month summer recess.

Ireland's government is planning a 2014 budget expected to feature 3.1 billion euros ($4 billion) in new cuts and tax hikes. The Irish already have endured five years of austerity following the collapse of their credit-driven Celtic Tiger boom in 2008.

Protesters moved from the parliament to nearby O'Connell Bridge, a key transport corridor. They outflanked a handful of officers and blocked both ends.