A U.S. Defense Department team detected signs of life in five locations, including one staffed by rescuers from Ecuador, but it's not clear whether anyone was pulled alive at those spots.

Maj. Gen. Daniel Allyn, the deputy commander of the Joint Task force Unified Response, said in a videoconference Tuesday from Haiti that he expected that transition to take place "very soon."

Among the places where rescue teams have been searching for Americans is the Hotel Montana, one of Port-au-Prince's most popular locations for visiting Americans. Among those thought to be buried there are four students and two faculty members from Lynn University, a private institution in Boca Raton, Fla. Eight other students escaped.

Haitian officials say that as many as 200,000 people may have died in the quake Jan. 12 and tens of thousands more were injured. International rescue teams have reported pulling fewer than 100 survivors from the rubble in the week since.

The latest developments came as the U.S. military faced mounting criticism about the pace of the rescue effort.

In response, the military announced Tuesday that it was opening two alternatives to Port-au-Prince's one-runway international airport for receiving aid: in Haiti's southern coastal city of Jacmel and in the adjoining Dominican Republic.

The USNS Comfort is expected to arrive Wednesday, Allyn said, joining four hospital ships from other nations that already are there.

Allyn said the number of U.S. troops in Haiti would double to 10,000 over the next several weeks.

On Tuesday, 800 Marines moved ashore west of Port-au-Prince, where they were planning to establish the first major aid-distribution center outside Haiti's capital since the earthquake struck.

The military also was working to create a network to provide safe drinking water, Allyn said.

On Monday, a C-17 aircraft flew from Pope Air Force Base in North Carolina and dropped nearly 15,000 meals and more than 15,000 liters of water in a field five miles northwest of the Port-au-Prince airport, the first such air delivery of aid since the earthquake hit. Another drop is scheduled for Wednesday, Allyn said. In all, the U.S. military has delivered 400,000 bottles of water and 300,000 food rations.

U.N. officials estimate that nearly 200,000 people of the 3.5 million affected have received food rations. As many as 1.5 million people are homeless, the U.N. has said, citing Haitian government statistics.

Allyn defended the U.S. effort, saying that Haiti's terrain and the level of destruction made finding drop points difficult. "Quite frankly, the earthquake did not take into account the location of drop zones," he said.

Pentagon commanders are considering how long U.S. troops will remain in Haiti, where the already frail government is barely functioning.

Allyn said the United States would stay as long as it was needed.

"We have the ability to fully sustain this," he said.