The appeal came as fighters from the Islamic State of Iraq and the Levant (ISIL) or alShaam (ISIS) were pressing a week-long offensive that has brought them close to the capital, and as Prime Minister Nuri al-Maliki pledging to face down "terrorism."
"Iraq has officially asked Washington to help under the security agreement (between the two countries), and to conduct air strikes against terrorist groups," Zebari told reporters in Saudi Arabia.
However, Zebari said "a military approach will not be enough. We acknowledge the need for drastic political solutions."
The United States spent millions of dollars over several years training and arming a new Iraqi army after disbanding the Sunni-led force created by the late dictator Saddam Hussein.
Washington has already deployed an aircraft carrier to the Gulf and sent marines to bolster security at its embassy in Baghdad, but President Barack Obama has insisted a return to combat in Iraq for US soldiers is not on the cards.
However, Secretary of State John Kerry has said drone strikes could be used.
Maliki vowed on television that "we will face terrorism and bring down the conspiracy," adding that "we will teach (militants) a lesson and strike them."
He also said the country's security forces, which wilted in the face of a major militant offensive that overran all of one province and chunks of three more in a matter of days last week, had suffered a "setback" but had not been defeated.
Maliki security spokesperson Lieutenant General Qassem Atta later said security forces would retake by Thursday morning full control of Tal Afar, a Shia dominant town in the north that lies along a strategic corridor to Syria.
That would provide a base from which to launch operations to recapture Mosul.
With regional tensions rising, Iranian President Hassan Rouhani said the Islamic republic "will do everything" to protect Shia shrines in Iraqi cities against the militant assault.
Saudi Arabia warned of the risks of a civil war in Iraq with unpredictable consequences for the region, while the United Arab Emirates recalled its envoy to Baghdad, voicing concern over "exclusionary and sectarian policies."
The crisis, which has displaced hundreds of thousands of Iraqis, threatens to break the country apart, while the assault on Baiji oil refinery Wednesday further spooked international oil markets.
Brent crude for August delivery added three cents to $113.48 per barrel just after midday in London.
US benchmark West Texas Intermediate for July delivery picked up 34 cents to $106.73 a barrel.
The attack on the refinery complex, in Salaheddin province north of Baghdad, was launched before dawn, officials said.
Atta said Iraqi forces managed to kill 40 militants and repel the attack, but that some tanks containing refined products caught fire.
The refinery was shut down and some employees evacuated on Tuesday due to a drop in demand caused by the militant drive.
World oil producers have cautiously watched the unfolding chaos in Iraq, which currently exports around 2.5 million barrels of oil per day. They have stressed that the country's vast crude supplies, mostly in the south, are safe for now.
The militants' swift advance has sparked international alarm, with the UN's envoy to Baghdad warning that the crisis was "life-threatening for Iraq."
Analysts suggested that the country could unravel, surviving at best as a federal state.
John Drake, an expert on Iraq with British security group AKE, was asked if Iraq could remain united.
"I don't think it's impossible, but it is highly unlikely," was his verdict.
Police and officials reported that militants had moved into the Shiite Turkmen area of Bashir in Kirkuk province and also seized three villages in Salaheddin province Wednesday.
Meanwhile, the Indian foreign ministry announced that 40 Indian construction workers had been abducted in Mosul, the first city to fall in the offensive.
Spokesperson Syed Akbaruddin said 46 Indian nurses were also stranded in the militant-held city of Tikrit.
There were reports of some Pakistanis among the construction workers abducted, but the Pakistani foreign office denied any Pakistanis were even in the area.
Last week, as the offensive got underway ISIL fighters kidnapped 49 Turks in Mosul, including diplomats and children, after earlier seizing 31 Turkish truck drivers.
In a bid to see off the offensive, Maliki sacked several top security commanders Tuesday evening, then stood alongside several of his main rivals in a rare display of unity among the country's fractious political leaders.
The dismissals came after soldiers and police fled en masse as insurgents swept into Mosul, a city of two million, on June 10.
Some abandoned their vehicles and uniforms when faced with the insurgents, which are led by ISIL fighters but also include loyalists of executed dictator Saddam Hussein.
After taking Mosul, militants captured a major chunk of mainly Sunni Arab territory stretching towards the capital.
Despite security forces' initial poor performance, Pentagon spokesman Rear Admiral John Kirby said Iraqi troops, with help from Shiite volunteers, were "stiffening their resistance" around Baghdad.
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@unbelievable: When America went to war in Iraq there were scores of media types "Embedded" with the troops! There were basic rules for the media types about not revealing their positions and not talking about tactics, but I remember eating and watching the war "live" on many channels! If Pakistan wants their war to be in the global news, then the army has to allow some media types to be on the front lines, otherwise there will be few takers for the droplets of news released by the ISPR flacks back in Rawalpindi!
Every international news outlet has this request as one of the top topics -- yet nobody is following the Pakistan "offensive" - gives you a taste of the limited press coverage Af-Pak is going to face when the American's pack up and leave.
Maliki said on Wednesday that the situation in Iraq is due to a conspiracy by certain political factions.
“You hear the Saudi and Qatar and some other Arab media calling them revolutionaries and that the Iraqi army is a sectarian force, but they’ve forgotten that they are living in countries brimming with sectarianism and marginalization of minorities," al-Maliki said, adding, We tell them and all our friends and Arab brothers to be sure that terrorism will never be limited to the Iraqi borders.”
Poor Iraq is actually asking the perpetrators and funders of ISIL. How can USA fund someone in Syria & attack the same people in Iraq.