Britain says it has begun tearing down some key security installations in response to the Irish Republican Army's decision to begin disarmament.

Britain's Northern Ireland secretary, John Reid, told Parliament Wednesday that work has already begun on demolishing some controversial military sites.

He said wrecking crews have started dismantling two army watchtowers in south Armagh, near the border with the Irish republic. On Thursday, he said, demolition will begin at an army base in County Derry and a police station in Armagh.

Mr. Reid says Britain will reduce its 13,000-man garrison in Northern Ireland over time.

"We will undertake a progressive, rolling program of security normalization, reducing levels of troops and installations in Northern Ireland as the security situation improves," he said.

The British announcement comes a day after an international disarmament commission confirmed the destruction of Irish Republican Army guns, ammunition and explosives.

Protestant and Catholic leaders alike are praising the IRA's decision, calling it unprecedented and historic.

The senior Protestant politician in Northern Ireland, David Trimble, is ending his party's boycott of the British province's power-sharing government.

Mr. Trimble had resigned as senior minister in July to protest the IRA's refusal to disarm and his actions had brought the Northern Ireland government to the brink of collapse.