Turkey has agreed to allow moderate Syrian rebels to be trained on its soil, the US says, in its bid to combat Islamic State in Syria and Iraq.
US National Security Adviser Susan Rice, who announced the development, said she welcomed the new agreement.
It has not yet been confirmed by Turkey, which has so far refused to send troops into Syria or Iraq.
And Turkey's PM says no deal has been reached to allow the US to use Incirlik air base to attack IS militants.
Turkish MPs recently passed a motion that could allow foreign forces to use its bases for activities in Syria and Iraq, although the final decision rests with the government.
The US-led coalition is carrying out air strikes against Islamic State militants, who have seized large parts of Iraq and Syria. Many have targeted IS around the key Syria-Turkey border town of Kobane.
Eight air strikes were launched by US and Saudi fighter jets on Sunday and Monday, with seven targeting IS near Kobane, US Central Command said.
Meanwhile, the UK-based Syrian Observatory for Human Rights monitoring group said an IS suicide bomber had detonated a truck with explosives to the north of the besieged Syrian Kurdish town on Monday.
IS militants, who control some areas of the town, are continuing to meet resistance from Kurdish forces there.
US military base
Speaking to US broadcaster NBC on Sunday, Ms Rice said Turkey had agreed to let the US use Turkish bases and territory "to train moderate Syrian opposition forces".
"That's the new commitment, and one that we very much welcome," she added.
Analysis: Mark Lowen, BBC News, Istanbul
We knew last week that Turkey would get involved in training moderate Syrian opposition groups - but at the time it seemed that would take place in Saudi Arabia.
Now, after a visit to Ankara by US presidential envoy John Allen, Susan Rice says the training will take place in Turkey. A US military delegation will be here this week to discuss details - and how Turkish bases can be used for the coalition operation against Islamic State.
However, the prime minister's office has now said that the US airbase at Incirlik in southern Turkey will not be used for strikes.
The training is a long-term goal. The coalition's immediate concern is the fate of Kobane and, on that, Turkey is still unwilling to intervene militarily.
It argues no other country wants to commit ground troops and it cannot deploy unilaterally, especially given its long, vulnerable border with Syria and Iraq.
And it wants the coalition to commit to targeting President Bashar al-Assad and creating a no-fly zone, neither of which are on the cards. So while Ankara is inching forward in the role it will play, nobody expects it to go into either country with guns blazing.
The training of Syria's moderate opposition is part of US President Barack Obama's anti-IS strategy announced last month.
In recent days, IS fighters have advanced against the Syrian town of Kobane, which has a border crossing point with Turkey.
But neither side has been able to gain significant ground.
Kurdish sources in Kobane said that fierce clashes continued on Monday near aid supplies warehouses at the south-west entrance to the town.
The militants were pushed back as they tried to advance towards a border crossing.
Turkey has ranged its military forces on the border but has so far ruled out any ground operation on its own and has refused to allow Kurds in Turkey to cross the border to fight.
Turkey has been reluctant to get involved militarily, partly because it is concerned about arming the Kurdish forces fighting IS militants. Turkey fought a long civil war with its Kurdish minority.
Since the IS offensive against Kobane began in mid-September, some 500 people have been killed and up to 200,000 have fled across the border into Turkey.
IS says it aims to establish a "caliphate", a state ruled by a single political and religious leader according to Islamic law, or Sharia.
It has become known for brutal tactics, including mass killings, abductions of members of religious and ethnic minorities, and the beheadings of soldiers and journalists.