The leaders of Britain and Ireland are calling on paramilitary groups in Northern Ireland to stop fomenting sectarian violence.

British Prime Minister Tony Blair and Irish Prime Minister Bertie Ahern met Friday to discuss the escalating violence in Northern Ireland.

Belfast, the capital of the British-ruled province, has been rocked by weeks of rioting and shootings between Catholics and Protestants. Police say paramilitary groups on both sides of the sectarian divide have been orchestrating the violence, including the Irish Republican Army, which has fought against the British in Northern Ireland.

The Blair-Ahern meeting came after British television quoted security officials saying the IRA has developed new bombs (in Colombia), even though the group is supposed to be observing a cease-fire under a 1998 peace accord.

The report sent jitters through the predominately Protestant unionist movement, which favors continued union between Northern Ireland and Britain. Prime Minister Blair is under pressure from some unionist leaders to declare the IRA in violation of the cease-fire, a move that could cripple the peace process.

After meeting the Irish prime minister, Mr. Blair told a news conference the IRA cannot take what he called just halfway steps toward peace and democracy.

"I understand the anxieties of the unionist community," he said. "That's why it is important that we make it very clear that there is no acceptable level of paramilitary activity. We are trying to move Northern Ireland away from paramilitary activity of any kind."

However, the British leader made it clear he does not want to do anything to jeopardize the peace accords. "We have come a long way in this process. And let's never forget that," Mr. Blair said. "I mean the peace process is in the end in my view still is the best guarantor of the end of paramilitary activity."

The Irish prime minister, Mr. Ahern, said it is time for leaders of both unionist and republican communities to step forward and demand an end to violence. "Everybody has a part to play in making sure that we can move on the positive agenda," he said. "And that means that we can have communities without friction, without violence. And that's what we are determined to do."

On another matter, the Irish leader briefed Mr. Blair on his efforts to allay public fears about Ireland's possible loss of military neutrality under a treaty aimed at expanding the size of the European Union.

Irish voters last year rejected the Nice Treaty, and the government is preparing to hold another referendum on the treaty later this year.