WASHINGTON (AP) - The top US military commander in Europe said on Tuesday that several Nato countries are working on contingency plans for possible military action to end the two-year civil war in Syria as President Bashar Assad's regime accused US-backed Syrian rebels of using chemical weapons.
The Obama administration rejected the Assad claim as a sign of desperation by a besieged government intent on drawing attention from its war atrocities - some 70,000 dead, more than 1 million refugees and 2.5 million people internally displaced.
A US official said there was no evidence that either Assad forces or the opposition had used chemical weapons in an attack in northern Syria.
The Republican chairman of the House Intelligence Committee, Mr Mike Rogers, said there was a "high probability" that the Assad government had used chemical weapons, although it was not clear whether he was referring to the attack in northern Syria.
"We need that final verification, but given everything we know over the last year and a half, I would come to the conclusion that they are either positioned for use, and ready to do that, or in fact have been used," Mr Rogers told CNN.
As the war enters its third year, the US military, State Department officials and the UN high commissioner for refugees delivered a dire assessment of a deteriorating situation in Syria and the sober view that even if Mr Assad leaves, the Middle East nation could slip into civil strife and ethnic cleansing similar to the Balkans in the 1990s.
"The Syrian situation continues to become worse and worse and worse," Admiral James Stavridis, the commander of US European Command, told the Senate Armed Services Committee.
Adm Stavridis, who is retiring soon, said a number of Nato nations are looking at a variety of military operations to end the deadlock and assist the opposition forces, including using aircraft to impose a no-fly zone, providing military assistance to the rebels and imposing arms embargoes.
As with US and international involvement in Libya in 2011, a resolution from the UN Security Council and agreement among the alliance's 28 members would be necessary before Nato assumes a military role in Syria, he said.
"We are prepared if called upon to be engaged as we were in Libya," he said.
But within individual member countries, the admiral said "there's a great deal of discussion" about lethal support to Syria, no-fly zones, arms embargoes and more.
"It is moving individually within the nations, but it has not yet come into Nato as an overall Nato-type approach," he said.
Nato has installed Patriot missile defence batteries in southern Turkey along the border with Syria that are also capable of shooting down aircraft. During an exchange with Senator John McCain, a Republican, Adm Stavridis said the Patriots could be positioned in such a way as to shoot down Syrian aircraft, and he indicated that doing so would be a powerful disincentive for pilots to fly in that area.
Turkey's leaders have been "very emphatic" that the missiles be used only for defensive purposes, he said. To use the batteries for other missions, including attacking Syrian military aircraft, would require consensus among Nato's members - "and we're far from that," he told the committee.
He said that his personal opinion is that providing military assistance to the Syrian opposition "would be helpful in breaking the deadlock and bringing down the Assad regime."
Syria's state-run news agency said 25 people were killed in a chemical attack on the Khan al-Assad village in northern Aleppo province. It said 86 people were wounded, some critically, and published pictures of children and others on stretchers in what appeared to be a hospital ward.
Russia, which has steadfastly supported Mr Assad in Syria's civil war, on Tuesday backed his assertion of a chemical attack.
White House spokesman Jay Carney said the US is looking carefully at all allegations but that the Obama administration is "deeply skeptical" of any claims emanating from Mr Assad's regime.
Mr Denis McDonough, the White House chief of staff, said the US wouldn't stand by if it turns out the regime used chemical weapons, but he declined to say whether he believed the reports could be true.
"If this is substantiated, it does suggest ... that this is a game-changer. And we will act accordingly," Mr McDonough told CNN. "This is something we take very, very seriously."
Syria has one of the world's largest arsenals of chemical weapons and Washington has been on high alert since last year for any possible use or transfer of chemical weapons by Mr Assad's forces.
It feared that an increasingly desperate regime might turn to the stockpiles in a bid to defeat the rebellion or transfer dangerous agents to militant groups such as Lebanon's Hezbollah, which the Syrian government has long supported.
At the time, officials noted movement of some of the Syrian stockpiles but said none appeared to be deployed for imminent use. Still, President Barack Obama declared the use, deployment or transfer of the weapons to be his "red line" for possible military intervention in the Arab country.