Vice President Joe Biden called Nuri al-Maliki for the second time this week as US pressure mounted on the Iraqi premier over an Al-Qaeda surge in the violence-plagued country.

Biden urged Maliki on Wednesday to "continue the Iraqi government's outreach to local, tribal, and national leaders," following the loss of Fallujah to Islamist insurgents, the White House said in a statement.

Spokesman Jay Carney meanwhile said Washington was pressing Maliki, a Shiite, to focus on political reconciliation as well as taking military action to expel Al-Qaeda-inspired groups from Fallujah and Ramadi, both Sunni bastions in Anbar province, once liberated from extremists by US troops.

Secretary of State John Kerry pressed home a similar message in a call with Iraqi Foreign Minister Hoshyar Zebari, the State Department said.

The calls came amid discussion in Washington foreign policy circles about who should take the blame for the resurgence of Al-Qaeda, especially in Fallujah and Ramadi, where American troops fought some of their most pitched battles since the Vietnam war.

Critics of the White House blame President Barack Obama for failing to agree a deal with Maliki's government to leave a residual US force behind after withdrawing all American troops from Iraq at the end of 2011.

But some US critics fault Maliki for not reaching out to Sunnis in Iraq, and for fostering discord that resulted in a vacuum that could be filled by groups such as the Islamic State of Iraq and the Levant (ISIL).

An alliance between US forces and Sunni tribes opposed to mostly foreign Al-Qaeda fighters was partly responsible for the success of a troop surge strategy in Anbar, a western province that borders Syria, in 2007 and 2008. Now Washington wants Maliki to adopt similar counter insurgency tactics.

Fallujah and parts of nearby Ramadi have been outside government hands for days -- the first time militants have exercised such open control in major cities since the height of the insurgency that followed the 2003 US-led invasion.

Biden also told Maliki that he welcomed his commitment that Iraqi elections would be held as scheduled for the end of April, despite a recent uptick in violence in Anbar, and against citizens in Iraqi cities.

"Prime Minister Maliki updated the Vice President on the situation in Anbar province, including a series of political initiatives that are under way at the local and national level," the statement said.

"The Vice President underscored that America will support and assist Iraq in its fight against international terrorism."

The United States said on Monday it would speed up deliveries of missiles and surveillance drones to Iraq.

The accelerated delivery will include 100 more Hellfire missiles, and an extra 10 ScanEagle surveillance drones -- a low-cost three-meter aircraft capable of flying for 24 hours.

Some 75 Hellfire missiles were delivered to Baghdad in mid-December, US officials said.

Kerry has however vowed that no American forces would return to Iraq to assist in military operations.

His spokeswoman Jen Psaki said that in his exchange with Zebari, Kerry called on Iraq's government to ensure that extra military support be twinned with "political and economic efforts to isolate extremist groups."