The United States and Australia have announced an agreement to maintain U.S. forces on Australian soil.

Australian Prime Minister Julia Gillard announced the terms of the agreement at a news conference Wednesday with U.S. President Barack Obama.

She said the deal called for a force of 200 to 250 U.S. Marines to be based in northern Australia for rotating six-month deployments. She said the force would grow over time to a full force of 2,500 personnel.

She said the agreement also opens Australian bases to U.S. aircraft. Mr. Obama said the agreement will better allow the United States to respond to a range of humanitarian and disaster needs as well as security challenges.