DUBLIN, Ireland - British prosecutors have charged a 61-year-old Irishman with the 1982 IRA attack on the queen's cavalry in Hyde Park, a nail-bombing at a London tourist attraction that left four soldiers and seven horses dead.

Wednesday's surprise arraignment of John Downey in a London court came on the 15th anniversary of the ratification of the Good Friday peace accord for Northern Ireland, which sought to end three decades of bloodshed over the disputed British territory.

British authorities declined to explain why they arrested Downey as he arrived Sunday at London's Gatwick Airport nearly 31 years after the attack.

Sinn Fein demanded Downey's immediate release. The Irish nationalist party accused Britain of violating an agreement not to pursue Downey, who had been on a list of IRA suspects "on the run" from British investigators.

Sinn Fein official Gerry Kelly called Downey's arrest "vindictive, unnecessary, and unhelpful" and an act of "bad faith" by the British government.

The IRA's main faction, the Provisional IRA, killed nearly 1,800 people during a failed 1970-97 campaign to force Northern Ireland out of the United Kingdom. Antiterrorist police in London and Northern Ireland, including a special "cold cases" unit, have continued to investigate unsolved IRA killings despite the Provisionals' 2005 decision to renounce violence and disarm.

These sporadic arrests of IRA veterans, often with Sinn Fein ties, have repeatedly raised tensions in the peace process, which remains incomplete as IRA splinter groups continue to mount occasional bombings and shootings.

Kelly, who led the IRA's first car-bomb attacks on London in 1973, said Downey had received a 2007 letter from Britain's Northern Ireland Office saying he was not wanted for questioning by any British police force and had traveled to London many times since then. Britain's Northern Ireland Office declined to comment on this.

In 2001, Britain agreed to give IRA fugitives from justice an amnesty so they could return to Northern Ireland without fear of arrest and prosecution, but the government later reneged because lawmakers refused to back the deal.