WASHINGTON - President Barack Obama has no plans to join a global treaty banning landmines because a policy review found the United States could not meet its security commitments without them, the State Department said on Tuesday.

An Iraqi soldier walks past confiscated ammunition and weapons after a raid operation in Baghdad, September 2, 2009. (REUTERS/Saad Shalash/Files) "This administration undertook a policy review and we decided that our landmine policy remains in effect," spokesman Ian Kelly told a briefing five days before a review conference in Cartegena, Colombia on the 10-year-old Mine Ban Treaty.

"We determined that we would not be able to meet our national defense needs nor our security commitments to our friends and allies if we signed this convention," he said.

It was the first time the administration had publicly disclosed the decision.

The treaty bans the use, stockpiling, production or transfer of antipersonnel mines. It has been endorsed by 156 countries, but the United States, Russia, China and India have not adopted it.

U.S. Senator Patrick Leahy, a leading advocate for the treaty, called the decision "a default of U.S. leadership."

"It is a lost opportunity for the United States to show leadership instead of joining with China and Russia and impeding progress," Leahy, a Vermont Democrat, said in a statement.

Landmines are known to have caused 5,197 casualties last year, a third of them children, according to the Nobel Prize-winning International Campaign to Ban Landmines (ICBL), which links some 1,000 activist groups.

The United States generally abides by the provisions of the treaty. It has not used antipersonnel mines since the 1991 Gulf War, has not exported any since 1992 and has not produced them since 1997, Steve Goose, director of the Arms Division of Human Rights Watch, told a briefing on Monday.

The review conference next Sunday is expected to draw more than 1,000 delegates representing more than 100 countries, including ministers and heads of state.

It will look at the progress of a broadly popular treaty that has helped cut landmine casualties around the world and provided relief to victims.

Kelly said the United States would send humanitarian mine relief experts from the State Department, Defense Department, U.S. Agency for International Development and the Centers for Disease Control and Prevention to observe the conference.

"As a global provider of security, we have an interest in the discussions there," Kelly said. "But we will be there as an observer, obviously, because we haven't signed the convention, nor do we plan to sign the convention."

U.S. SENDING OBSERVERS

It is the first time the United States has sent observers to a gathering of states that have accepted the treaty, a move that was welcomed by anti-landmine campaigners.

"The very fact that they are showing up we take as a positive sign of movement on this issue within the Obama administration," Goose said.

"We hope they're not coming empty-handed," he added. "We very much want them to come and say that they intend to join this convention. Even if they can't give a timeline, we want them to say they intend to join at some point in time."

Anti-mine campaigners said a declaration of intent was important because the Bush administration reversed U.S. policy on accepting the convention and said it would never join.

While Kelly's comment indicated no shift in administration policy, Jeff Abramson, deputy director of the nonpartisan Arms Control Association, said the United States was expected to make a statement at the conference that might shed more light on the decision.

He said it would be disappointing if such a statement shut the door to continuing a review of U.S. policy.

Kelly said the United States was the world's single largest financial supporter of humanitarian mine action, having provided more than $1.5 billion since 1993 to support mine clearance and destruction of conventional weapons.

In contravention of the treaty, however, the United States stockpiles some 10 million antipersonnel mines and retains the option to use them.

But using mines would pose big problems for Washington, Goose said, because most of its allies including all but one NATO country, are parties to the treaty and are pledged not to help other countries use the weapons.

(Editing by Sandra Maler and Alan Elsner)