Arsonists attacked 10 Catholic churches overnight, wrecking three, in a campaign linked to rising sectarian passions over Northern Ireland's most divisive march.

Police and politicians blamed the attacks on thugs determined to punish British authorities for telling the Orange Order, Northern Ireland's major pro-British Protestant fraternal group, not to march through the main Catholic section of Portadown this weekend.Fearful that rising tensions could undermine April's peace agreement, British Prime Minister Tony Blair flew into Belfast Thursday to meet top political and religious leaders and to inspect at least one of the damaged churches.

Blair's spokesman, Alastair Campbell, said the prime minister would emphasize that Northern Ireland's future lay in "dialogue and democracy, not violence."

Nine churches targeted early Thursday were in isolated and predominantly Protestant rural areas between Belfast and Portadown, 30 miles to the southwest. Another church, in overwhelmingly Protestant east Belfast, suffered minor damage.

Also Thursday, gasoline bombs were thrown at two Catholic homes on the predominantly Protestant east side of Londonderry, Northern Ireland's second-largest city. Flower pots were thrown through the windows of another Catholic-occupied home on north Belfast's staunchly Protestant Shore Road. No one was hurt.

No group claimed responsibility for any of the attacks, but police linked them to members of an outlawed pro-British gang, the Loyalist Volunteer Force. The group, based in Portadown, called a cease-fire in May after coming under intense police pressure, but opposes the entire peace process.

"It is appalling that people have returned to this type of activity at a time when new political horizons are emerging," said Adam Ingram, Britain's minister responsible for security and victims in Northern Ireland.

The Protestant and Catholic politicians elected Wednesday to head Northern Ireland's new compromise government jointly condemned the violence.