US troops deployed to West Africa to fight the Ebola outbreak could stay up to a year, depending on how quickly the virus can be contained, a top general said Tuesday.

The head of the US military's Africa Command, General David Rodriguez, also rejected criticism that the American response to the crisis has been too slow, saying the troop deployment had to be designed to take into account Liberia's limited infrastructure.

About 350 US troops have arrived in Liberia and Senegal so far as part of a 3,200-strong force due to to help with logistical support, training for health workers and mobile test labs.

Asked how long American troops would remain in the region, Rodriguez told reporters: "I'm sure it'll be about a year ... at this point, but that's just a guess."

He said that "we'll have to play that by ear" and see how fast transmission rates decline.

US government experts believe that if 70 percent of patients infected with Ebola could be moved to treatment facilities, the spread of the virus could be curtailed, the four-star general said.

"Then at that point, they believe the curve will start going down. And then it will be based on how fast and how effectively, one, the curve turns down and, two, the international community can then pick up all the requirements," he said.

US forces in Monrovia have established a headquarters to oversee the mission and set up several mobile medical labs to increase "the capacity for rapidly diagnosing Ebola," he said.

Rodriguez vowed to ensure that US troops heading to Liberia would undergo special training, wear protective gear and work under "strict" medical protocols to avoid contracting the deadly virus.

The Pentagon has said US troops would not have any direct contact with Ebola patients, but officials said Tuesday that a small number of personnel would handle blood samples in testing labs.

Critics and some aid workers have accused President Barack Obama's administration of moving too slowly in response to the epidemic, questioning why it is taking weeks to deploy troops.

Rodriguez, however, said the pace was dictated in part by Liberia's limited infrastructure and that moving too many troops too quickly would be counter-productive.

"As you can imagine, their infrastructure and their capacity to house people, to feed people, and all that, is limited," he said.

"We just don't want to overwhelm them and press things in there that they can't absorb at all."