Northern Ireland police have raided offices and homes of members of the Sinn Fein party. Authorities call it a crackdown on spying by the Irish Republican Army. Police say they arrested at least four activists of Sinn Fein, the political wing of the IRA. The raids come at a critical moment for the Northern Ireland peace process.

About 200 police officers took part in the raids that began at dawn Friday.

Several homes and offices of Sinn Fein activists were searched near Belfast. The main target was Sinn Fein's office at Stormont, the headquarters of the Northern Ireland assembly. Police arrested the party's administrator, Denis Donaldson and seized some computer disks.

Senior Sinn Fein party official, Bairbre de Brun, denounced the raids and said the police had no warrant. She is particularly upset that the news media were tipped off to the raids.

"This is clearly for media consumption and its clearly politically inspired to try and halt the progress of change," she said. "It's anti-democratic, it's anti-Sinn Fein, it's anti-peace process and it's anti the process of change which must continue in this country and which will continue in the country."

Police offered few details about who or what they were looking for. But the head of the Northern Ireland government, David Trimble, says the IRA is apparently continuing spy operations.

"What we know so far, or suspect so far, is that there has been an IRA intelligence operation directed against the upper echelons of the government, having penetrated the Northern Ireland office, and maybe having penetrated other things as well," Mr. Trimble said.

Mr. Trimble, head of the biggest party opposed to the IRA, says he will meet British Prime Minister Tony Blair in London early next week to discuss the matter.

Mr. Trimble is threatening to leave government in January if the IRA continues to be implicated in political violence in the long-troubled province.

If he carries out the threat, it would be a major blow to the 1998 Good Friday agreement that set up power-sharing between unionists, who favor continued British rule over Northern Ireland, and republicans who want the province to merge with the Republic of Ireland.