"The worst thing is to take things and let them sit on the ground and rot," Harry K. Thomas Jr., the State Department's executive secretary, said in Washington.
For four days, a C-130 transport plane ready to lift emergency supplies to Katrina victims has stood idle at the Satenas air force base in southern Sweden.
The aid includes a water purification system that may be urgently needed amid signs deadly diseases may be spreading through fetid pools in New Orleans, and blankets for those left homeless.
"We have to get some kind of signal (from the United States) in the next few days," said Karin Viklund of the Swedish Rescue Services Agency. "We really hope we will get it."
More than a week after Canada first offered to send military support, three Canadian warships and one coast guard ship departed for the Gulf Coast on Wednesday.
Although the government in Ottawa has been careful not to criticize the slow response, newspaper editorials asked why Washington seemed reluctant to accept Canadian aid.
The United States has accepted offers of nearly $1 billion in assistance from some 95 countries, Thomas said.
In Switzerland, aid officials expected an answer to their aid offer by Tuesday night. They met Wednesday afternoon to discuss what to do while waiting for a response.
Poland, Austria and Norway also had not heard back on their aid offers, and countries in Asia also were waiting for replies.
India, which regularly is hit by flooding unleashed by monsoon rains, has a planeload of supplies waiting but nowhere to send it.
"The plane is parked at the airport here and we are awaiting instructions on where to send the medicines and food items," an External Affairs Ministry official said Wednesday, declining to be identified under government briefing rules.