Roughly 20,000 U.S. troops will be supporting relief efforts in Haiti by Jan. 24, military officials said, adding to the 13,000-strong American force currently there.

Comprising the force will be the 22nd Marine Expeditionary Unit, the 82nd Airborne Division's 2nd Brigade and thousands of other troops operating afloat off the Haitian coast and on shore, distributing provisions, assisting in medical operations and helping to maintain security. Some 2,200 Marines of the 24th MarineExpeditionary Unit are slated to arrive within 48 hours, military officials said.

"The 24th Marine Expeditionary Unit is a huge part of enabling us to extend our reach to places around the country that may need our assistance but we just haven't been there yet," Army Lt. Gen. P.K. Keen, the top U.S. commander in Haiti, said on The Pentagon Channel today.

The additional forces come as international aid continues pouring into Haiti following a magnitude 7 earthquake that struck Jan. 12, creating what an official called one of the greatest humanitarian emergencies in the history of the Americas.

About 2,000 Marines of the 22nd Marine Expeditionary Unit that came ashore earlier this week have zeroed in on an area west of Port-au-Prince where much of the larger destruction occurred, according to Air Force Gen. Douglas Fraser, the commander of U.S. Southern Command.

In the meantime, some 1,400 flights are waiting to land at the congested Toussaint Louverture International Airport in the capital of Port-au-Prince, where the United States is overseeing upwards of 140 flights daily asofficials look to open additional airfields, Fraser told Pentagon reporters today. Reports of bottlenecking at the airport have emerged as its capacity has swelled from an average of 13 commercial aircraft daily arrivals before the quake.

As of yesterday, an airport about 30 miles southeast of the Haitian capital in the city of Jacmel became operational in addition to the San Isidro airport in neighboring Dominican Republic, where officials are looking to open a third airport in Maria Montez.

Officials say the disaster has killed between 100,000 to 200,000 people and the Red Cross estimates some 3 million people have been affected. To date, the United States has delivered 1.4 million bottles of water, 700,000 meals and 22,000 pounds of medical equipment, which are being disbursed among some 100 distribution sites, Fraser said.

While the cost of relief efforts is difficult to estimate given its scope, Fraser placed the figure at $100 million. The Defense Department pledged up to $20 million in emergency relief funds in days forHaiti, and sprang troops into action following the quake.

Off the Haitian coast are 20 U.S. ships, with the floating hospital vessel USNS Comfort among them, adding medical capabilities and supplying about 600 medical personnel and 1,000 desperately needed hospital beds. As of yesterday, roughly 270 U.S. medical personnel on the ground had treated more than 5,100 people inHaiti.