ISLAMABAD, Pakistan  The Pakistani Taliban called the presence of foreign relief workers in this flood-ravaged country “unacceptable” on Thursday and suggested that militants could attack members of aid groups.

Any violence would add more strain to relief efforts that have been slow to reach the millions of Pakistanis uprooted by the worst flooding in the country’s history.

A spokesman for the United Nations dismissed the threats, saying that its aid work remained unaffected by security worries. But the State Department said it was concerned that militants “may well” attack foreign aid workers or Pakistani government officials trying to help flood victims.

“It is a real threat,” a State Department spokesman, P. J. Crowley, said at a briefing in Washington.