US military aircraft have dropped weapons, ammunition and medical supplies to Kurdish fighters battling Islamic State (IS) militants in the key Syrian town of Kobane.
US Central Command said C-130 transport aircraft made "multiple" drops of supplies provided by Kurdish authorities in Iraq.
US air strikes have helped push back IS in the town near the Turkish border.
Correspondents say the airdrops are likely to anger key US ally Turkey.
The drops of supplies provided by Kurdish authorities in Iraq were "intended to enable continued resistance against Isil's attempts to overtake Kobane," Centcom said in a statement. IS is also referred to as Isil and Isis.
All the aircraft involved had returned safely, it added.
CentCom says US forces have conducted more than 135 air strikes against IS in Kobane since early October.
"Combined with continued resistance to Isil on the ground, indications are that these strikes have slowed Isil advances into the city, killed hundreds of their fighters and destroyed or damaged scores of pieces of Isil combat equipment and fighting positions," the Centcom statement said.
However, it added that IS fighters continued to threaten Kurdish forces' ability to resist and hold the city. "Kobane could still fall," it said.
Senior Washington officials said the airdrops had involved three planes and 27 bundles of supplies.
On Sunday, Turkish President Recep Tayyip Erdogan said he would not allow Kurdish fighters to receive any transfers of American arms.
Turkey has resisted calls to help the Kurds fighting in Kobane, describing them as terrorists like the Kurdish militant group the PKK.
Turkey has faced a decades-long insurgency by the PKK, which is also regarded as a terrorist group by the US and the European Union.
A US administration official said President Barack Obama had called Mr Erdogan on Saturday to inform him that the airdrops would be taking place. The official did not say how Mr Erdogan reacted.
Analysis: Guney Yildiz, BBC Turkish
The US air drops represent a significant shift in Washington's policy towards the Syrian Kurds.
Syrian Kurdish fighters confounded the bleak predictions about Kobane's imminent fall, and the air drops are now taking place despite objections from the Turkish government: Turkish President Recep Tayyip Erdogan had said his country would not agree to any US arms transfers to Syrian Kurdish fighters.
Nevertheless, the US state department recently declared that it had held the first direct talks with the Syrian Kurdish Party - considered an ally of the Kurdistan Workers' Party (PKK), which fought a three-decade war against the Turkish army until 2013.
US officials have previously said that they had to limit their relations with the Kurds in Syria due to objections from Turkey.
Weeks of fighting
The rapid advance of IS in both Syria and Iraq, where it controls large chunks of territory, has rattled the West prompting the US-led air strikes.
Kobane is a strategic objective for IS, and fierce fighting has raged in the town for weeks, forcing the evacuation of most of its civilian inhabitants.
The IS advance in Syria takes place against the backdrop of the civil war. US-led air strikes are being conducted there without the permission of President Bashar al-Assad, who the West wants to relinquish power.
In Iraq, the air campaign is taking place with the co-operation of the government. The advance of IS there earlier this year has taken it to close to the capital, Baghdad.
The key northern Baiji oil refinery is under constant IS threat, and on Sunday the Iraqi military said it was carrying out an offensive to retake the nearby city of the same name.
Neighbouring Iran is seen as a key ally of the Baghdad government in the fight against IS and Iraqi PM Haidar al-Abadi is scheduled to visit Tehran on Monday for talks on the conflict. However, Iran is not part of the US-led coalition.
In another sign of how the IS threat is worsening sectarian tensions in Iraq, a suicide bomber killed 19 people and wounded another 28 outside a Shia mosque in Baghdad on Sunday.
Baghdad has seen an increase in bomb attacks in recent weeks - many claimed by IS.
- Formed out of al-Qaeda in Iraq (AQI) in 2013, IS first captured Raqqa in eastern Syria
- It captured broad swathes of Iraq in June, including Mosul, and declared a "caliphate" in areas it controls in Syria and Iraq
- Pursuing an extreme form of Sunni Islam, IS has persecuted non-Muslims such as Yazidis and Christians, as well as Shia Muslims, whom it regards as heretics
- Known for its brutal tactics, including beheadings of soldiers, Western journalists and aid workers
- The CIA says the group could have as many as 31,000 fighters in Iraq and Syria