Vice Adm. Thad Allen of the Coast Guard, left, who was placed in charge of the Hurricane Katrina recovery, speaks in October with a resident of Bayou La Batre, Ala. Sen. John Ensign, R-Nev., has placed a hold on Allen's nomination for a promotion. Photo by The Associated Press.

WASHINGTON -- Sen. John Ensign is blocking a promotion for Vice Adm. Thad Allen, the Coast Guard chief of staff put in charge of the Hurricane Katrina response in September.

In the hurricane's aftermath, Ensign, a Republican, expressed concern about the evacuation and handling of pets stranded in the disastrous Gulf Coast flooding.

Ensign, a veterinarian, flew on Sept. 28 to Louisiana and met with Allen, who had been installed to take over the federal disaster response from Michael Brown, the criticized director of the Federal Emergency Management Agency.

Ensign spokesman Jack Finn on Monday said that Ensign "overall was disappointed with the effort down there, but he felt things improved after his visit."

Finn confirmed that Ensign has placed a hold on Allen's nomination to become an admiral and the Coast Guard's commandant.

Finn would not say why or whether the senator's action was related to Katrina or the pet rescues.

Ensign "has some additional questions for the nominee," Finn said.

The Senate Commerce Committee held a confirmation hearing with Allen on March 9 and approved his confirmation by voice vote on Thursday.

Ensign's hold, first reported by Congressional Quarterly, would prevent the full Senate from completing Allen's confirmation.

Ensign returned from the Gulf region in September expressing optimism and saying Allen had promised to hire people as soon as possible to coordinate animal welfare matters.

Ensign argued that hungry stray dogs would form packs and pose threats to rescuers and returning families and would pose potential health problems.

Animal welfare activists faulted federal responders for lack of guidelines and consistency on how pets were handled during evacuations of flooded neighborhoods.

In some cases, rescuers refused to allow pets to accompany their owners in rescue boats and evacuation buses, causing some people to stay behind with their animals.

If Ensign's hold is tied to the animal rescue efforts, "that is an issue we consider a worthy subject of the Senate's attention," said Wayne Pacelle, president and chief executive of the Humane Society of the United States.

"There were millions of Americans focused on animal welfare issues in the wake of the disaster, and we also know the bungled federal response to the animal crisis undermined the effectiveness of the human rescue mission," Pacelle said.

Volunteers rescued more than 10,000 animals after Hurricane Katrina, Pacelle said.

Pet rescue centers established in Gonzales, La., and Hattiesburg, Miss., handled 7,500 animals, mostly cats and dogs, but also a few turtles and some pet mice.