The US Defence Department has said the US military has conducted an airstrike against Islamic State fighters near the northern Iraqi city of Erbil.

A Pentagon statement said two F/A-18 warplanes dropped 225 kilograms of laser-guided bombs on a mobile artillery piece which “[the Islamic State] was using … to shell Kurdish forces defending Erbil where US personnel are located.”

“The decision to strike was made by the US Central Command commander under authorisation granted him by the commander in chief,” it said.

Al Jazeera’s Jane Arraf, reporting Erbil, said: “Fighters have captured US-made weapons as Kurdish troops withdrew from various regions. Washington also wants to address that.”

US President Barack Obama on Thursday authorised air strikes against Islamic State fighters in Iraq, who have taken over large areas of the country, saying the measure was meant to avert “genocide”.

“We can act, carefully and responsibly to prevent a potential act of genocide,” Obama said on Thursday, referring to the Yazidis, a religious minority group besieged by fighters from the Islamic State.

Several thousand Yazidis, members of an ancient pre-Muslim religious minority, are stranded on high ground in the north after being driven out of their home town of Sinjar by Islamic State fighters.

Shia cleric calls for unity

The armed group, which is also active in Syria, has been advancing in various parts of Iraq, fighting against troops from the Kurdish and central governments.

The group sees Iraq’s Shia Muslims and minorities such as Christians and Yazidis as infidels.

Meanwhile. Iraq’s senior Shia cleric Ayatollah Ali Sistani has called on Iraqis to unite to confront the threat of the Islamic State group.

“All Iraqis should unify ranks and intensify efforts in the face of this big danger that threatens their present and future,” said Sistani.

In what will be interpreted as a criticism of the Prime Minister Nouri Al-Maliki, he also said those clinging to their positions were making a grave mistake. Al Jazeera