Baghdad (AFP) - A rocket attack in Iraq killed a US civilian contractor, raising fears on Saturday that violence could escalate in the protest-hit country already engulfed in its worst political crisis in decades.

Washington recently promised "a decisive US response" to a growing number of unclaimed attacks on its interests in Iraq, which it blames on pro-Iran factions.

US-Iran tensions have soared since Washington pulled out of a landmark nuclear agreement with Tehran last year and imposed crippling sanctions.

Baghdad -- which is close to both countries -- risks being caught in the middle.

A barrage of 30 rockets was fired at the K1 Iraqi military base in Kirkuk, an oil-rich region north of Baghdad, around 2220 GMT Friday, a US official told AFP.

"One US civilian contractor was killed and several US service members and Iraqi personnel were wounded," said the US-led international coalition against the Islamic State group.

A direct hit on an ammunition depot caused secondary explosions, and four more rockets were found in their tubes in a truck at the launch point, the US official told AFP on condition of anonymity.

Federal security forces, Shiite militia units and IS sleeper cells all have a presence in Kirkuk province, which is claimed by both Iraq's autonomous Kurdistan Region and federal authorities.

Following the attack, "an escalation is possible but it is far from certain," said Iraq expert Fanar Haddad at Singapore University's Middle East Institute.

"More importantly, anyone pushing for an escalation in (Washington) DC will have to contend with (President Donald) Trump's aversion to increased military engagement in the Middle East."

- Protest paralysis -

The attack comes as Iraq is gripped by its biggest anti-government street protests since the US-led invasion of 2003 that toppled dictator Saddam Hussein.

Protesters, many of whom grew up in the post-Saddam era, have vented their anger at a government they consider inept, corrupt and beholden to neighbouring Iran.

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Violence has claimed about 460 lives, most of them protesters, and left some 25,000 people wounded, but rallies and sit-ins have continued.

Demonstrators on Saturday blocked a road to an oil field in Nasiriyah, in southern Iraq, halting production for the first time since protests started in early October.

If sustained, such shut-downs could have a major impact in OPEC's second largest producer, which depends on oil exports averaging 3.6 million barrels a day.

The protests forced the resignation of the Iraqi government nearly a month ago. Since then, Iran and its local allies have pushed to select the next prime minister, sparking more anger and threats by the president to quit.

- 'Very accurate' -

The political unrest has coincided with an increase in rocket and mortar attacks against American interests in Iraq.

Ten attacks since October 28 have left several Iraqi military personnel wounded and one dead and caused damage around the US Embassy in Baghdad's ultra-secure Green Zone.

Five rockets hit Al-Asad air base on December 3, just four days after US Vice President Mike Pence visited troops there. More than a dozen rockets hit the Qayyarah air base in northern Iraq in November.

In Friday's attack, a Kirkuk provincial security official told AFP, "the shots were very accurate. The attack was aimed precisely at the area where the Americans are located, near the meeting room".

A US source has said pro-Iran factions in Iraq are now considered a more significant threat to American soldiers than IS, whose sweeping offensive in 2014 saw Washington deploy thousands of troops to the country.

Reflecting this concern, "a convoy of 15 American vehicles each carrying armour and weapons" recently arrived at the US embassy in Baghdad, according to an Iraqi security official.

US diplomatic and military sources have told AFP of their growing frustration with the recent attacks.

They say they rely on their Iraqi partners to play a "de-conflicting" role between American forces and the Hashed al-Shaabi, an umbrella organisation for paramilitary groups largely made up of Iran-backed Shiite militias.

That is a complicated task, as the Hashed has been ordered to integrate with the regular security forces, but many of its fighters continue to operate with a degree of independence.