WASHINGTON - American special operations forces have started a programme to train Syrian rebels with the intention of deploying them in the country to fight against Islamic State forces, the Pentagon has said.

Defence officials said the rebels have been carefully screened and are being trained as a politically moderate fighting force - something that is currently lacking in Syrian fighters, the New York Times reported. The training is being conducted in Jordan.

So far, though, the group is small - about 90 rebels. But the Pentagon’s aim is to establish the training programme and supply a steady source of sophisticated fighters to combat the powerful Islamic State. Nearly 4,000 Syrian rebels have already volunteered for the programme, officials said.

“We’re starting with the people that we have that we have vetted carefully. We’re figuring out what the best training is, what the initial deployment is,” Defence Secretary Ashton Carter said.

The Pentagon said it hopes the training programme will grow over time and supplement fighting by other rebels, some of whom are already being trained and deployed by the Central Intelligence Agency.

However, rebels have often faced shortages of troops and weapons as they try to go up against thousands of IS fighters and the Nusra Front. Some CIA-trained rebels have even switched allegiances to the IS, officials said.

Once the programme is fully operational, US officials hope to train about 5,000 rebel fighters per year - who will receive other American support, if needed, like airstrikes and surveillance.

The Pentagon said that it will likely take years to compile a rebel force large enough and sophisticated enough to counter the Islamic State movement.

It is not yet known exactly how the first group of trained rebels will be deployed in Syria, or how the Pentagon will respond if they are targeted by Syrian President Bashar Assad’s regime, the Times report said.

About 400 rebels have been admitted to the programme, and they will receive training, pay and small arms at sites in Turkey, Jordan, Saudi Arabia and Qatar, defence officials said.

President Barack Obama announced the training programme last year.”This is a complex programme,” Carter said. “It’s going to have to evolve over time.”