The United States has offered Nicaragua healthcare aid in exchange for the destruction of 657 Soviet-made missiles acquired to fight US-backed rebels in the 1980s, the US ambassador said here.

Washington has long pressured Nicaragua to destroy the anti-aircraft missiles as part of a global effort to remove old weapons that could fall into the hands of terrorists.

The exchange deal was prepared "by a team from the (US) Department of Defense specialized in the administration of hospitals, medicines, and technical equipment," who recently visited the country, and the Nicaraguan health ministry, said US ambassador Paul Trivelli on a television news program late Sunday.

It was now up to Nicaraguan President Daniel Ortega, who proposed the medical-missile exchange last year, to sign the deal to hand over 657 of some 1,000 missiles still held, Trivelli said, without detailing the medical aid.

Ortega has said he would keep some 400 missiles for national security reasons.

The SAM-7 missiles are remnants of the civil war between Ortega's Sandinista National Liberation Front and US-backed Contra rebels in the 1980s.

Former Nicaraguan president Enrique Bolanos destroyed 1,000 such missiles in 2004.

Ortega, a former Marxist guerrilla and Cold War-era foe of the United States, was elected for a second term in 2006.