US Defense Secretary Chuck Hagel on Saturday extended the stay of US F-16 warplanes and Patriot missile-defense batteries in Jordan past their use in joint military drills later this month, according to The Wall Street Journal.
The Journal said the extension could lay the groundwork for a conflict-free zone between US ally Jordan and Syria, where a more than two-year civil war threatens to spillover into the region.
The US and Jordan are set to hold military exercises there together at the end of June, reported Reuters.
The White House this week approved military aid for Syria's rebel movement, a force trying to overthrow Syrian President Bashar al-Assad as part of a conflict that has taken tens of thousands of lives.
According to the Journal, the US would work primarily from Jordan to supply the rebels with aid.
The news comes as Russia's foreign minister on Saturday said any possible US-led effort to establish a no-fly zone over Syria would violate international law.
Sergei Lavrov, at a news conference in Moscow, said "leaks from Western media" had shown US F-16 fighters and Patriot missile to be in Jordan, and that these weapons could be used in neighboring Syria against President Bashar al-Assad's forces.
"You don't have to be a great expert to understand that this will violate international law," Lavrov said.
The Kremlin, Syria's stalwart ally, had previsouly said it would send advanced surface-to-air missiles and MiG-29 fighter jets to Damascus. It's unclear when or if those weapons were sent, and if they have arrived.
The US and its allies have hesitated to arm the various factions of the Syrian opposition with advanced weapons like anti-aircraft missiles for fear they would end up arming Islamist insurgents linked to al Qaeda.