The Pentagon announced that a mission to train the “moderate” Syrian opposition may involve over 1,000 US troops. The first soldiers may flow into the region in a month, while the trained fighters may return to Syria to “fight ISIS” by the end of 2015.

The earlier announced number suggested 400 pairs of US boots on the ground in countries neighboring Syria, where the training will take place. However, Pentagon spokesman John Kirby told reporters in a press briefing on Friday that the total number "could approach 1,000."

"It might even exceed that. I can't rule that out," Kirby added.

The troops, ranging from special operations to conventional forces, will be based in at least three different training sites – in Saudi Arabia, Qatar, and Turkey.

Deployment orders could come as early as next week, with full deployment beginning in the next four to six weeks, Kirby said.

“I think you’ll start to see orders for some of those troops over the next four to six weeks. Some could be given orders very soon, perhaps as soon as within the next week or so. But they'll flow in, I think, over the next four to six weeks,” he added.

However, Kirby said that recruiting has not yet started, and that opposition training would not begin before March.

The US is “working with the Syrian moderate opposition leadership to identify potential Syrian moderate groups from which recruiting could occur,” Kirby explained. After that, the rebels will have several months of training before they are sent into battle by the end of the year.

The training mission, according to Pentagon officials, will focus on reaching three goals.

First of all, the US plans to train the opposition in self-defense to protect the towns they control. Secondly, the US envisages the “moderate” opposition eventually starting an offensive against Islamic State forces. And finally, Kirby said, the trained fighters would “help work with political opposition leaders towards a political solution in Syria.”

Kirby also announced that trainers from other countries could join the effort to help tackle the Islamic State threat in Syria.

The $500 million training plan for Syrian insurgents was first proposed by the Pentagon in June last year. Congress first approved the measure in September for three months, and last month has extended the program through 2016.