WASHINGTON - Secretary of State Hillary Rodham Clinton has introduced former United Nations ambassador Richard Holbrooke to be a special envoy to Afghanistan and Pakistan.

In making the announcement, Clinton said anything short of a "relentless diplomatic effort" in the region will fail.

She said Holbrooke's challenge would be to co-ordinate U.S. efforts in the region, including those of the Pentagon.

Holbrooke noted that Pakistan and Afghanistan have "different histories" and traditions, yet find themselves inextricably linked.

Referring to the Taliban and al-Qaida, he said both countries are waging a difficult struggle against an "enemy without any scruples" in the tribal areas along their shared border.

Holbrooke pledged to bring coherence to foreign assistance efforts he described as "chaotic."