The training of about 3,000 Free Syrian Army officers, which began at a Jordanian military base last year, has been stepped up and expanded after rebel gains in southern Syria, the officials told The Washington Post.
Instead of completing the training in June, it will be completed this month, in light of the victories, including along the Syrian-Jordanian border near the Golan Heights, two military outposts and the country's main border crossing with Jordan, Jordanian security officials told the newspaper.
Jordan is on Syria's southern border.
U.S. and Jordanian officials said they were increasingly concerned moderate rebel forces, responsible for many military wins in the south and around the Syrian capital Damascus, would be overtaken by extremist Islamic fighters who now dominate many parts of northern Syria under rebel control.
"The last thing anyone wants to see is al-Qaida gaining a foothold in southern Syria next to Israel. That is a doomsday scenario," a U.S. diplomat in Jordan told the Post.
Israel is on Syria's southwestern border.
The possible buffer zone in southern Syria would seek to convert rebel-controlled areas into permanent havens for Syrian army defectors and displaced civilians and allow easy access for humanitarian aid, the officials said.
Keeping the displaced civilians in the zone could also help Jordan, a country of 6.5 million people that has taken in more than 470,000 refugees fleeing the Syrian civil war.
The refugee number in Jordan is expected to rise to 1 million by the end of the year, U.N. High Commissioner for Refugees Antonio Guterres said last month.
He said Washington would provide an additional $200 million in aid to help Jordan care for the refugees.
The Obama administration and regional governments have expressed fears the Syrian fighting may soon spill over into other countries -- and have said a buffer zone could prevent it from spilling into Jordan.