SAN JOSE (AFP) - United States President Barack Obama came close to ruling out deploying troops to Syria, saying he did not foresee a scenario in which that would be beneficial to the United States or Syria.
"As a general rule, I don't rule things out as commander-in-chief because circumstances change and you want to make sure that I always have the full power of the United States at our disposal to meet American national security interests," said Mr Obama, speaking during a visit to Costa Rica late Friday.
"Having said that, I do not foresee a scenario in which boots on the ground in Syria - American boots on the ground in Syria - would not only be good for America but also would be good for Syria."
Speculation has mounted that the Obama administration could reverse its opposition to arming the rebels after the White House said last week that President Bashar al-Assad likely used chemical weapons on his people.
Mr Obama has been reluctant to intervene in the war but faces mounting criticism that he has allowed the Assad regime to cross his own declared "red line" on using chemical weapons.
The US president has stressed that more proof is needed for the United States to step up its involvement in a civil war that has already claimed more than 70,000 lives and is now in its third year.
Mr Obama said there was evidence that chemical weapons had been used in Syria, but that "we don't know when, where or how they were used."
But he noted that any strong evidence of the Assad regime using such weapons would be a "game changer" because they could fall into the hands of groups like the militant group Hezbollah, based in neighbouring Lebanon.
"In terms of any additional steps that we take, it is going to be based on, number one the facts on the ground, number two it's going to be based on what's in the interest of the American people and our national security," Mr Obama said.
He emphasised that he would "make those decisions based on the best evidence and after careful consultation."
Experts say a military mission to secure the chemical weapons would require a large ground force and pose huge risks, with the outcome hinging on the quality of Western intelligence.
Former Pentagon chief Leon Panetta, who stepped down in February, had told lawmakers that he and the US military's top officer, General Martin Dempsey, had recommended arming the rebels but were overruled.
In Syria, meanwhile, US media reported that Israel conducted an airstrike targeting a weapons shipment headed for Hezbollah based in neighboring Lebanon.
White House and Pentagon officials declined to comment on the reports.
CNN said that US and Western intelligence agencies were reviewing information suggesting Israel likely conducted the strike overnight Thursday to Friday.
A senior US official told NBC News that the airstrikes were likely tied to delivery systems for chemical weapons, though CNN, citing officials, said it was unlikely that Israel had struck chemical weapons storage facilities.
But Republican Senator Lindsey Graham of South Carolina, who serves on the Senate Armed Services Committee, was quoted as saying at a Republican Party fundraising dinner in his state that Israel had indeed bombed Syria.
"Israel bombed Syria tonight," Senator Graham was cited by the Politico news website as saying in passing, without offering any further details.