The Peruvian air force plane opened fire as a last resort

Peruvian Defence Ministry

The plane crashed near the town of Pebas, about 1,130km (700 miles) north-east of Lima.

The Peruvian defence ministry said the plane had been mistaken for a drug trafficker's aircraft because it had not filed a flight plan and had not responded to international warnings.

This has been denied by the missionary group.

Missionary Veronica "Ronnie" Bowers, 35, and her seven-month-old adopted daughter, Charity, were both killed.

Pilot Kevin Donalson was wounded. Also on board but unhurt were Bowers' husband, Jim Bowers, 35, and their six-year-old son Cory.

A Pennsylvania-based missionary group, the Association of Baptists for World Evangelism, said the plane carrying its workers was being flown by an experienced pilot and was clearly marked.

The Peruvians may have thought plane carried narcotics

A spokesman told the BBC he had been informed that the plane caught fire in the attack.

However, it had landed on the River Amazon, where it was fired on again.

The Peruvian Defence Ministry said the plane ignored international identification procedures.

"After carrying out international identification and interception procedure - which the pilot ignored - the Peruvian air force plane opened fire as a last resort," the ministry said in a statement.

American embassy to investigate

The plane was spotted by an air surveillance system run jointly with the United States to control drugs trafficking.

The missionary organisation said a flight plan was filed, and that the pilot had just requested permission to land at Iquitos when it was fired on.

It has been reported that the missionary family had lived and worked in the Amazon area for nearly 10 years.

The American embassy in Lima has sent officials to investigate the incident.

"We deeply regret this tragedy and are in the process of determining the extent of loss of life and injury to the passengers and crew," a State Department official said.

Drug planes shot in past

The jungle area where the plane was shot down is close to the border with Colombia, where left-wing guerrillas and drug smugglers are active.

Between 1994 and 1997, Peru shot down about 25 suspected drug planes on their way from camps in the Peruvian Amazon to Colombian cocaine refineries.

The US is pouring millions of dollars into a controversial war against drugs in the region.