Fifteen soldiers were killed this week guarding an oil pipeline in northern Iraq, the first assault to involve so many casualties amid concerns an al-Qaida insurgency in western Iraq is spreading to vital oil-producing regions.

Iraqi security authorities said Tuesday's attack on the camp in Nineveh province took place the same day that Iraqi security forces captured three al-Qaida suspects as they tried to blow up a pipeline near the northern Kirkuk oilfields, which hold about a third of Iraq's oil reserves of 431 billion barrels. Twin pipelines that carry Kirkuk's oil production to Turkey's Ceyhan terminal on the Mediterranean for export are a frequent target for saboteurs.

Hussein al-Shahristani, Iraqi's deputy prime minister for energy, told reporters in Baghdad Jan. 28 Iraq's oil industry, the country's economic lifeline, is increasingly coming under attack because of the civil war in neighboring Syria in which Iraqi jihadists are battling the regime of President Bashar Assad.

One of the largest rebel forces is the Islamic State for Iraq and the Levant, a Sunni offshoot of al-Qaida in Iraq, which is also waging an escalating campaign inside Iraq against the Shiite-dominated government of Prime Minister Nouri al-Maliki.

There have been signs ISIL is extending its war, been centered on Iraq's three western provinces, which are overwhelmingly Sunni, to the north, like Nineveh, dominated by Sunnis, Kurds and other minorities.

"Attacking the energy sector has been among their top priorities to deprive the country of its main revenue sources," Shahristani said. "The attacks have been focused on oil export pipelines, power generation and transmission lines."

There have been some attacks in Shiite-dominated Basra province in the south where Iraq's biggest oil fields are, but these have so far had little impact on the energy industry in the area dominated by major international oil companies such as BP, Exxon Mobil, Total of France and Italy's Eni, which are seeking to boost production to unprecedented levels.

Iraq is currently the second largest producer in the Organization of Petroleum Exporting countries after Saudi Arabia, with an output of about 3 million barrels per day, of which 22 million barrels are exported.

Shahristani, who as oil minister was the architect of Iraq's drive to rebuild its dilapidated energy industry following the 2003 U.S.-led ouster of Saddam Hussein, says Baghdad aims to triple production to 9 million bpd by 2020.

But that could be impeded by the worsening security situation and fears Iraq is headed for all-out sectarian warfare between the majority Shiites, backed by Iran, and the Sunni minority who are in a rebellious mood because of a nationwide government crackdown.

Sunnis make up about a third of Iraq's 32 million population.

Sharistani admitted the fighting in western Iraq, most notably in Anbar province where al-Qaida fighters seized much of the cities of Fallujah and Ramadi Dec. 31, is hampering Baghdad's efforts to develop the Qayara and Najmah oil fields, as well as in Nineveh in the northwest, an al-Qaida stronghold.

The foreign oil companies have long complained Baghdad's notorious infrastructure bottlenecks and slow-moving bureaucracy are often more of a hindrance than the security threat.

But all this is stifling efforts to boost production and Baghdad's plan to show the biggest annual rise in oil exports since the U.S. invasion of March 2003.

Nevertheless, oil analysts say as long as the violence can be kept out of the vast southern megafields like Rumeila, West Qurna 1 and Majnoon, Iraq can maintain an acceptable production level.

But with some 8,000 people killed by U.N count in 2013, the bloodiest year in Iraq since 2008, and 2014 already looking like it will be just as bad, if not worse, there doesn't seem to be any relief in sight for the oil industry, or the country as a whole.

Maliki's energy problem is further compounded by the semiautonomous Kurdish enclave across three northeastern provinces, which has started exporting its oil to Ceyhan through a Turkish-built pipeline rather than through the Baghdad-controlled state network.

This has heightened tensions between the Kurdish Regional Government and Baghdad, already enflamed over the Kurds' claim to the Kirkuk oilfields just south of their heavily armed enclave, and cut into Iraq's overall output at a critical time.