US planes have made humanitarian aid drops to the besieged Iraqi town of Amerli, the Pentagon has said.
Some 15,000 minority Shia Turkmen in Amerli have been surrounded by Islamic State (IS) militants for two months.
The US also carried out air strikes on IS positions. The Iraqi army, Shia militias and Kurdish fighters have been struggling to break the siege.
Aircraft from the UK, Australia and France joined the US in the humanitarian aid drops, said Rear Admiral John Kirby.
Food, water, and medical supplies were delivered.
Rear Adm Kirby said operations would limited in scope and duration, as required to protect civilians trapped in Amerli.
The UN has expressed fears there could be a massacre if IS breaks through defences in the town, which lies in Kurdish-controlled Iraq.
Earlier, the US launched new air strikes on IS near the key Mosul Dam.
In a statement, the US military said an armed vehicle, a fighting position and weapons were destroyed in the raid.
It said the strikes were in support of operations conducted by the Iraqi security forces near the strategic dam in the north of the country.
IS has been accused of atrocities in areas of Iraq and Syria under its control.
The Shia Turkmen are seen as apostates by the IS militants.
Thousands of people have been trapped in the town for two months, though it is believed there are fewer than previously estimated.
The BBC reports the combined forces are mounting an assault on two fronts in the Salahuddin Kurdish area in northern Iraq.
From the south, Iraqi government troops and allied Shia militias are trying to push into the Marin hill, which overlook the plain on which Amerli lies.
With the help of air strikes by the Iraqi air force, they are reported to be making slow progress, with roads in the area heavily mined and booby-trapped by the Islamist militants.
From further north, a combination of army forces, Shia militia and Kurdish Peshmerga fighters is reported to be trying to push down towards Amerli through a string of villages held by IS.
The operation is reported to have two objectives: to break the siege of Amerli and to reopen the main highway leading north from Baghdad.
Australian Govt says it's acting in national interest
The Australian Government says it's acting in the national interest by sending air force planes to carry weapons into northern Iraq.
The United States wants Australian planes based in Dubai to fly munitions and arms to Kurdish fighters battling Islamic State militants.
Prime Minister Tony Abbott has agreed to a request from the United States for an Royal Australian Air Force plan to join an international team dropping weapons and military equipment to forces fighting Islamic State militants.
Immigration Minister Scott Morrison said that the Cabinet carefully considered the risks of further involvement in Iraq's civil war.
The ABC reports that Royal Australian Air Force planes have already dropped humanitarian aid into Amerli.