US Vice President Joe Biden has called Nouri al-Maliki, the Iraqi prime minister, to express concern about the political climate in Baghdad amid a deepening political crisis, the White House said.
Tariq al-Hashemi, Iraq's Sunni vice president, denied accusations on Tuesday that he organised death squads, describing the charges as a trumped-up case brought only after the departure of US troops.
Biden, who visited Iraq earlier this month ahead of the pullout of American forces, said the US was monitoring conditions in Iraq closely and remained committed to a long-term strategic partnership.
"The vice president also stressed the urgent need for the prime minister and the leaders of the other major blocs to meet and work through their differences together," the White House said in a statement.
The issuing of an arrest warrant for Iraq's highest-ranking Sunni politician and rising ethnic tensions have raised questions about the stability of the country just days after the end of a nearly nine-year war.
The latest intrigue threatens to tear apart Iraq's coalition government and perhaps kick-start another Sunni uprising.
It also raises suspicions that Maliki, a Shia, ordered the arrest of the vice president as part of a campaign to consolidate his hold on power out of a fear that Sunnis in and out of Iraq are plotting against him.
Sunnis, the minority Muslim sect in Iraq, feared a new round of sectarian warfare could result from the charges, announced the day after the last American soldiers left the country.
The accusations date back to the height of the war in 2006 and 2007, when neighbours turned on neighbours and whole
sections of Baghdad were expunged of one Muslim sect or the other.
Kurdish leaders were trying to work out a solution, sheltering Hashemi from arrest in their semi-autonomous region in northern Iraq.
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"I swear to God that Hashemi didn't commit any sin or do anything wrong against any Iraqi either now or in the future and this is my pledge to God," Hashemi said at a press conference in which he accused Maliki of ordering the warrant.
He described the confessions of his bodyguards that aired on Iraqi state TV as "fabricated" and the charges as a campaign to "embarrass" him.
"Maliki is behind the whole issue. The country is in the hands of Maliki. All the efforts that have been exerted to reach national reconciliation and to unite Iraq are now gone. So yes, I blame Maliki," he said.
Hashemi spoke from the Kurdish city of Irbil, where he traveled on Sunday after learning that authorities were preparing to arrest him.
Although the Kurdish region is part of Iraq, Hashemi is probably safe from Baghdad's reach, as Kurdish leaders run their own security affairs.
The Iraqi army and national police do not travel there, and Maliki would be reluctant to ask the Kurds, a powerful political bloc that he needs, to return Hashemi for prosecution.
Most Kurds are Sunni Muslims, but they are a different ethnic group from the Arabs that make up the majority of Iraq's population.
Hashemi has said he might leave Iraq temporarily and has often traveled to neighbouring Turkey.
Many lawmakers in his Sunni-backed Iraqiya political bloc have essentially made Jordan their second home.
On Monday, state-run television aired what it characterised as confessions by men said to be bodyguards for Hashemi.
The men said they killed officials working in the health ministry and foreign ministry as well as Baghdad police officers, and that they received $3,000 from Hashemi for each attack.
Maliki effectively runs the Interior Ministry, where the charges originated.
Iraqiya has repeatedly accused the Shia prime minister of hoarding power and last weekend boycotted parliament because Maliki refused to give up control over key posts.
"The political process is on the brink of disaster because of the decisions made by the government in the past two days," Jasim al-Halbusi, a member of the predominantly Sunni Anbar Provincial Council, said.
"There are some people who have to understand that Iraq cannot be ruled by one sect," he said, alluding to Maliki's Shia allies.