The United States says it will send a small number of special operations forces to Syria that will advise rebels but that the deployment will not be a combat mission.
The October 30 announcement came amid a call by the United States, Russia, and other countries for the UN to launch a new diplomatic effort to halt the 4 1/2-year war in Syria.
White House spokesman Josh Earnest told reporters in Washington that U.S. President Barack Obama had ordered the deployment of fewer than 50 commandoes to assist moderate forces opposed seeking to oust Syrian President Bashar al-Assad.
"Those special operations forces will be in Syria and they'll be offering some training, some advice, and some assistance to moderate opposition forces that are fighting ISIL in northern Syria right now," Earnest said, using an acronym for the militants known as the Islamic State (IS) group.
A senior U.S. official told reporters at the Pentagon that the special operations forces will arrive in northern Syria within the next month to start their advisory mission, which, according to the official, will stop short of accompanying fighters on operations against the extremist Islamic State (IS) group.
But Defense Secretary Ash Carter warned that the decision to send special operations forces to Syria will put U.S. forces in harm's way.
"Our role fundamentally and the strategy is to enable local forces but does that put U.S. forces in harm's way? It does, no question about it," Carter said during a visit to Alaska.
Earlier this month a U.S. soldier was killed in Iraq while taking part in a Kurdish-led mission to rescue IS hostages.
The deployment marks the first time that U.S. military forces will operate openly on the ground in Syria, though Earnest stressed that the action was not a combat mission.
"If we were envisioning a combat operation, we probably would be contemplating more than 50 troops on the ground," he said.
Joshua Landis, director of Center for Middle East studies at University of Oklahoma, told Reuters news agency that the move was not a game-changer.
"This is tinkering around the edges and it does up America's role and it will allow America to go to the Iraqis and go to the Russians and everybody and say we are doing more, but it doesn't fundamentally change anything," Landis said.
U.S. Senator John McCain (Republican-Arizona), an outspoken critic of Obama's foreign policy, said the decision to deploy special forces in Syria was not sufficient to degrade and destroy the IS group.
"Such grudging incrementalism is woefully inadequate to the scale of the challenge we face," McCain, who chairs the Senate Armed Services Committee, said in a statement.
Western news agencies quoted unidentified U.S. officials as saying earlier in the day that Washington would be sending additional aircraft, including F-15 fighters and A-10s, to Turkey's Incirlik air base.
The U.S. decision comes after Russia escalated its military role in Syria to support Assad.
Earlier in the day, Russian Deputy Foreign Minister Sergei Ryabkov said Moscow considered the use of U.S. forces without coordination with Assad's government unacceptable.
Russia has conducted a campaign of air strikes in Syria since September 30, targeting enemies of Assad.
'Progress' At Vienna Talks
Meanwhile, U.S. Secretary of State John Kerry said in Vienna on October 30 that Washington, Moscow, and more than a dozen other countries have directed the United Nations to launch a new diplomatic process between Assad's government and the rebels.
Russia and Iran have been staunch supporters of the Syrian president, while Washington and its allies have insisted that he cannot be part of a postwar government.
Kerry spoke at a joint news conference with his Russian counterpart, Sergei Lavrov, following talks on Syria in the Austrian capital between diplomats from 17 countries, plus the UN and the European Union.
Neither the Syrian government nor Syrian rebel groups were represented at the talks.
Kerry said the timing of the White House's decision to deploy the small force to Syria was a coincidence and not tied to the talks in Vienna.
The October 30 meeting expanded talks that began in Vienna a day earlier and included Iran for the first time in efforts by world and regional powers to agree on how to end the Syrian crisis.
Others who took part in the talks include senior envoys from the United States, Russia, China, Britain, France, Turkey, Saudi Arabia, Iran, Iraq, Egypt, Lebanon, Jordan, Qatar, the United Arab Emirates, Oman, Germany, and Italy.
World leaders said progress had been made during the Vienna negotiations but that they remain divided over the fate of Assad.
They said another round of talks was to be held in two weeks' time.
Split On Assad
Kerry said he had "agreed to disagree" with his Iranian and Russian counterparts on Assad's future, adding that all three would continue to work together to pursue a political settlement.
Iran earlier said that it does not believe Assad must stay in power indefinitely.
"Iran does not insist on keeping Assad in power forever," Iranian Deputy Foreign Minister Amir Abdollahian, a member of Tehran's delegation, was quoted by Iranian media as saying.
French Foreign Minister Laurent Fabius said that "there are a number of points on which we agreed, notably on the transition process, the prospect of elections and how all this should be organized, and the role of the United Nations."
Reuters quoted sources close to the talks as saying that Iran favored a six-month "transition" period in Syria followed by elections to decide the fate of Assad.
Russian Deputy Foreign Minister Mikhail Bogdanov said Moscow wanted the Syrian opposition to agree upon a common approach and make-up of a delegation for talks with Damascus.
He said that Russia and Saudi Arabia had exchanged lists in Vienna of Syrian opposition figures to be potentially included in such talks, and that Russia wanted the Syrian Free Army and the Kurds to take part.
Russia, which has waged a month of intense air strikes against Assad's armed opponents, has also urged preparations for parliamentary and presidential elections in Syria.
But the idea has been rejected by rebels who say a vote would be impossible in the current circumstances, with millions of Syrians displaced, cities standing in ruins, and two-thirds of the country in the hands of jihadists and other armed groups.
Just ahead of the talks, more than 50 people were killed on October 30 when rockets fired by Syrian government forces hit a market in a rebel-held area outside Damascus, the Britain-based Syrian Observatory for Human Rights said.
Despite the wide differences in position at the Vienna talks, officials say the fact the meeting is taking place with so many countries is a sign that progress is possible.
With reporting by Reuters, AFP, and AP