* Fourteen car bombs explode in Iraqi capital
* Violence widely blamed on Sunni Islamist militants
* Arbil tense after first big attack in Kurdstan since 2007
By Kareem Raheem
BAGHDAD, Sept 30 (Reuters) - Car bombs killed at least 54 people in mostly Shi'ite Muslim areas of Baghdad on Monday as suspected Sunni Muslim militants pursued a campaign to plunge Iraq back into sectarian strife.
Altogether 14 bombs shook Baghdad, the deadliest of them in Sadr City, where a white car blew up near where men had gathered to seek work, killing seven people, including two soldiers.
"The driver said he would move the car soon, but it exploded a few minutes later," said Abu Mohammed, a worker at the scene, where bits of molten metal lay among cars wrecked in the blast.
Violence blamed mostly on Sunni militants who view Shi'ites as heretics has killed more than 6,000 people this year, according to the monitoring group Iraq Body Count, reversing a decline in sectarian bloodshed that had climaxed in 2006-07.
At that time, Sunni tribesmen helped U.S. forces rout al Qaeda, but many of those "Sahwa (Awakening)" fighters say the Shi'ite-led government has reneged on promises to reward them.
Their discontent reflects wider resentment among minority Sunnis against the government that came to power after the U.S.-led invasion that vanquished Saddam Hussein in 2003.
Sunnis launched street protests in December after Shi'ite Prime Minister Nouri al-Maliki sought to arrest a senior Sunni politician. A bloody raid by security forces on a protest camp in April touched off a violent backlash by Sunni militants.
"The (security situation) will get worse because al Qaeda and its allies will increase their attacks against both sects to incite people and force them to respond," said a senior security official who declined to be named.
So far Shi'ite militias, most of which disarmed in recent years and joined the reconstituted security forces or entered the political process, have largely held their fire, but several attacks in recent weeks suggest that some are retaliating.
Iraq's sectarian balance has come under further pressure from the civil war in neighbouring Syria, where mainly Sunni rebels are fighting to topple a leader backed by Shi'ite Iran.
Both Sunnis and Shi'ites have crossed into Syria from Iraq to fight on opposite sides of the conflict.
Al Qaeda's Iraqi and Syrian branches merged earlier this year to form the Islamic State of Iraq and the Levant, which has claimed responsibility for attacks on both sides of the border.
On Sunday, the Kurdistan region, a northern enclave relatively insulated from the violence that afflicts the rest of Iraq, suffered its first major bombing since 2007.
A charred crater in the road marks where a car bomb exploded during a suicide assault on the security headquarters in the regional capital Arbil in which at least six people were killed.
A stench of burnt tarmac still hung over the scene, and the remains of a slain assailant lay on the grassy road divider.
"We realise that Arbil is a big, attractive target for terrorists," said the city's governor Nozad Hadi. "During the past seven years there were constant attempts by terrorists to undermine the security of the capital."
Kurdistan's relative security has attracted some of the world's largest oil companies including ExxonMobil, Chevron Corp and Total to the region, which is autonomous and polices its own borders.
Most of these oil firms have their main offices in Arbil, but after Sunday's attack they took extra security measures and restricted the movements of their staff, industry sources said.
No group has claimed responsibility for the Arbil attack, but it was hailed by hardline Sunni Islamists, who in recent months have been fighting a Kurdish militia in Syria.
Analysts say the assault may have been carried out by al Qaeda-affiliated militants in revenge for the Kurdistan Regional Government's perceived support for Kurds in Syria.
A risk consultancy said militants would try to strike the region again, but would find it difficult because the Kurdish security apparatus is "relatively well developed".
"Further attacks should therefore be expected but they are likely to remain infrequent occurrences," said John Drake, of the AKE consultancy. "The day-to-day operating environment will remain stable but we will continue to warn against complacency."