The American military for the first time airdropped weapons, ammunition and medical supplies to Syrian Kurds in the battleground city of Kobane, US Central Command said on Sunday, in a move likely to anger key ally Turkey.
A C-130 cargo aircraft conducted "multiple" airdrops of the supplies provided by Kurdish authorities in Iraq.
The supplies were "intended to enable continued resistance against ISIL's attempts to overtake Kobane," CENTCOM said in a statement referring to Islamic State fighters.
The United States and its Western allies have been pressing Turkey to take a more direct role in taking on IS fighters in Kobane, but Ankara is reluctant to arm Kurds and intervene militarily against the militants, fearing an effective fighting force from its historic foes on its border.
Turkish President Recep Tayyip Erdogan earlier rejected calls for his country to arm the main Kurdish party in Syria, describing the group as a terrorist organization, linked to the outlawed Kurdistan Workers' Party (PKK), which has waged a 30-year insurgency for self-rule in southeastern Turkey.
But in a call, Erdogan and US President Barack Obama pledged to "strengthen cooperation" against IS in Syria.
American-led warplanes launched 11 air strikes near Kobane on Saturday and Sunday, CENTCOM said, helping Kurdish fighters repulse a new IS attempt to cut their supply lines from Turkey.
So far, US forces have conducted more than 135 airstrikes against IS in Kobane alone.
"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," CENTCOM said.
"However, the security situation in Kobane remains fragile as ISIL continues to threaten the city and Kurdish forces continue to resist."
CENTCOM Commander General Lloyd Austin has warned that the city could fall.
Kobane's Kurdish defenders have been under IS assault for more than a month.
From Saturday into Sunday morning, 31 IS militants died in the battle, said the Syrian Observatory for Human Rights.
Coalition air strikes near Kobane hit 20 IS fighting positions, five IS vehicles and two IS-held buildings, according to CENTCOM.
The Observatory, which has a network of sources inside Syria, said 15 fighters were killed in the air strikes, while 16 others died in ground clashes along with seven Kurdish fighters.