Several U.S. senators offered their support on Wednesday to five Belfast sisters who are campaigning against the Irish Republican Army's (search) killing of their brother, a case raising international pressure on the outlawed paramilitary group to disband.

"No political party can also have an armed unit that continues the violence and criminality in today's world," said Sen. Edward Kennedy, D-Mass., part of a growing chorus of Irish-American leaders who have rebuked the IRA over the Jan. 30 killing of Robert McCartney (search).

McCartney was beaten and stabbed to death outside a Belfast pub. His sisters have led a campaign to try to apprehend his killers, saying more than 70 potential witnesses are too afraid to identify anyone responsible to police because local IRA figures were involved.

"We hope that this does produce results on the ground for our family," said Catherine McCartney, standing beside her sisters Gemma, Claire, Paula and Donna.

Under increasing public pressure to cooperate, the IRA instead offered to shoot four of the men responsible, a move that only prompted further criticism.

Kennedy has refused to meet this week with Gerry Adams (search), chief of the IRA-linked Sinn Fein party. Adams also was not invited to traditional St. Patrick's Day ceremonies at the White House and Capitol Hill.

Kennedy instead stood shoulder to shoulder on Wednesday with the McCartney sisters and Sens. Hillary Rodham Clinton, D-N.Y.; Christopher Dodd, D-Conn.; and John McCain, R-Ariz.

The senators plan to offer a Senate resolution in support of the sisters.

The peace process in Northern Ireland (search), Clinton said, "cannot go forward unless there is a complete reckoning with the demand for justice in the murder of Robert McCartney."

While invoking the historic 1998 Good Friday peace accord (search) that was crafted in part by the Clinton administration, Sen. Clinton did not say whether she thought the IRA should disband, as Kennedy and other U.S. politicians have urged.

The sisters are hoping that public support in the United States for their cause will spur Sinn Fein (search) and the IRA to encourage witnesses to offer evidence directly to Northern Ireland's police force. The Sinn Fein-IRA movement, which rejects police authority, instead has advised witnesses to offer statements to lawyers, a widely criticized policy in Northern Ireland.

Their first appointment Wednesday was with Mitchell Reiss, the Bush administration's special envoy to Northern Ireland, who repeated his calls for the IRA to disarm and disband.

"Seven years after the Good Friday agreement and four years after 9/11, it's time for the IRA to close shop and go home to their families," Reiss said.

Gemma McCartney said the purpose of the visit was to "keep the pressure on" until the men responsible for killing their brother are charged and convicted.