An aid worker sits on bags of flour as Pakistanis line up for supplies being handed out by the United Nations World Food Program at a camp for displaced families in Sukkar in southern Pakistan. The UN is reviewing security measures after a warning that Taliban insurgents are planning to attack foreigners. (Kevin Frayer/Associated Press)

The United Nations says it's reviewing security measures for its aid workers helping with flood relief efforts in Pakistan.

The move comes after a warning from the U.S. that Taliban insurgents are planning to attack foreigners there. The sense from Washington is that the threat is both serious and credible.

It focuses on Tehrik-e Taliban, which is considered the most radical and violent militant group in Pakistan. The group is based in the tribal region close to the border with Afghanistan.

It has been associated with a series of attacks in recent years on the Pakistani state and on foreigners and is closely allied to al-Qaeda.

In the last the six months, the level of violence has reduced, but since the flood crisis began, the Pakistani Taliban has warned against accepting international aid. Its leaders seem to view accepting foreign assistance and the presence of international aid workers as welcoming foreign interference in their country.

Pakistani Taliban spokesman Azam Tariq said Thursday that the United States and other countries were not really focused on providing aid to flood victims but had other "intentions" he did not specify.

Tariq strongly hinted that the militants could resort to violence.

"When we say something is unacceptable to us one can draw his own conclusion," he said.

Tariq spoke with The Associated Press by telephone from an undisclosed location.

Complicates flood relief effort

All of this is a further blow to aid workers who are already battling plenty of logistical challenges. The UN says more than 17 million people have been affected by the floods, and about 1.2 million homes have been destroyed, leaving five million people homeless.

The overall threat to the security of foreign aid workers was always in the background, but the flood crisis has brought it to the forefront.

United Nations spokesman Maurizio Giulano said the international organization cannot let violent threats deter its relief effort.

"There is a lot of work ahead and millions of people who need our assistance," said Giulano. "We would find it inhumane for someone to target us and our work, effectively harming the millions of people whose lives we strive to save."