Updated

Calling the devastation in Haiti "extraordinary," President Obama on Friday pledged long-term reconstruction help to President Rene Preval as up to 10,000 U.S. troops headed to Haiti's shores to help distribute aid and prevent potential rioting among desperate earthquake survivors.

"The entire world stands with the government and the people of Haiti," Obama said from the White House. "For in Haiti's devastation, we all see the common humanity that we share."

Obama urged Americans to be patient with relief efforts there.

"There will be many difficult days ahead," he said.

Obama, who had been unable to contact Preval several times this week, said he talked for 30 minutes with the Haitian leader.

Obama told Preval the world has been devastated by the loss and suffering and pledged full U.S. support for both the immediate recovery effort and the long-term reconstruction. Preval said that the needs in his country are great, but that aid is now making its way to the Haitian people. Preval ended the call with a message to the American people, saying "from the bottom of my heart and on behalf of the Haitian people, thank you, thank you, thank you."

Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, also said the total American presence in and around the beleaguered country could rise beyond the 10,000 expected to arrive Monday as U.S. military officers determine how much assistance may be needed in the days ahead.

His assessment came as the State Department updated the toll of U.S. dead from Tuesday's 7.0 magnitude quake to six and cautioned that the casualty count is likely to rise still further.

State Department spokesman P.J. Crowley said that in addition to the previously reported death of agency employee Victoria DeLong, there have been at least five other confirmed U.S. deaths -- all private U.S. citizens whose names have not been released publicly.

"And that number is going to go up," Crowley told reporters without offering a specific forecast.

DeLong, a cultural affairs officer at the U.S. Embassy, was killed when her home collapsed in the earthquake.

In a joint news conference at the Pentagon with Mullen, Defense Secretary Robert Gates said the primary goal is to distribute aid as quickly as possible "so that people don't, in their desperation, turn to violence." He suggested that the U.S. is aware of perceptions it could have too-high a profile in the ravaged country.

"I think that if we, particularly given the role that we will have in delivering food and water and medical help to people, my guess is the reaction will be one of relief at seeing Americans providing this kind of help," Gates told reporters.

The secretary also said "there will be a lot of other people there as well," noting Brazil also has a significant presence. He said it was vital to get food and water into the country and called the security situation "pretty good," except for some isolated cases of scavenging for food and water.

The secretary said military planners have been reluctant to drop food and water packages from the air because it could lead to lead to rioting. But bringing in supplies by sea and air have proved difficult because of Haiti's badly damaged sea port and congested airport.

Crowley, the State Department spokesman, acknowledged the limitations of the initial U.S. effort to get water, food and other emergency requirements into Haiti. He said, for example, that the main port at Port-au-Prince, the capital, was so badly damaged in the quake that it is not useable. He likened the stream of aid thus far as flowing through a "garden hose" that must be widened to a "river."

The arrival off the Haitian coast of the USS Carl Vinson, an aircraft carrier laden with helicopters, essentially provides a "second airport" from which aid can be delivered to the stricken capital, Crowley said.

As of Friday morning, 846 of the approximately 45,000 Americans in Haiti had been evacuated from the country, Crowley said. Another 160 were at the U.S. Embassy in Port-au-Prince awaiting evacuation, he added.

Gates said the U.N. peacekeeping force in Haiti has primary responsibility for security in the capital.

Mullen said the hospital ship USNS Comfort, with hundreds of medical professionals and medical support, should be off the Haitian coast by the end of next week.

"While these assets tend to the immediate material and medical needs of the people of Haiti, these ships, aircraft and troops also deliver hope, although it seems that supplies and security cannot come quickly enough," Mullen said.

The Associated Press contributed to this report.