The United States hailed the nomination of a new Iraqi prime minister as a "key milestone" today, and offered to step up help in rolling back gains by Islamic militants.

Vice President Joe Biden made the offer in a call to Iraqi President Fuad Masum, who had earlier asked Haidar al-Abadi to form a new government, replacing that of incumbent premier Nuri al-Maliki.

In a second call the vice president also relayed US President Barack Obama's congratulations to Mr Abadi and restated "his commitment to fully support a new and inclusive Iraqi government."

According to the White House, Mr Abadi told Biden he intended "to move expeditiously to form a broad-based, inclusive government capable of countering the threat of the Islamic State of Iraq and the Levant, and building a better future for Iraqis from all communities."

In his call to Mr Masum, Mr Biden commended the Iraqi president "for meeting this key milestone" of asking Mr Abadi to form a more inclusive new government.

The move, which comes after months of political wrangling, is likely to be resisted by Mr al-Maliki.

He has indicated he will not cave in to pressure to drop a bid for a third term, with his allies claiming that Mr Abadi has no legitimacy.

UN Secretary-General Ban Ki-moon has welcomed what he described as "the forward movement toward government formation in Iraq".

He also praised the Iraqi president's decision to ask Mr al-Abadi to form a new cabinet, the United Nations said.

Meanwhile, European Union envoys are to meet tomorrow for an emergency meeting over the deepening crisis in Iraq, an EU diplomatic source said.

The source said that envoys from the EU's member states would meet in Brussels in order "to coordinate as well as possible" a response to the latest advances by Islamist militants across Iraq.

French Foreign Minister Laurent Fabius has called on the EU to "mobilise" to respond to appeals from Iraq's Kurds for arms to fight Islamic State jihadists.

In a letter to EU foreign affairs representative Catherine Ashton, Mr Fabius said: "It is crucial that the European Union mobilises from today to respond to this appeal for help."

The United States is exploring options to evacuate thousands of Iraqi civilians trapped on a barren mountain in northern Iraq by Islamic militants, after four nights of humanitarian relief air drops.

The air drops appear to have provided urgently needed aid.

However, the harsh conditions of the Sinjar mountain range in mid-summer have taken scores of lives among Iraq's Yazidi minority, who are threatened by Islamic State militants.

RTE