* Blast on crude, condensate pipelines to Zueitina port
* Libya oil sector already hurt by protests, strikes
* Investigation to be completed next week
By Marie-Louise Gumuchian and Ghaith Shennib
TRIPOLI, April 18 (Reuters) - A probe into an April 2 blast on pipelines to the Libyan oil port of Zueitina points to sabotage, industry sources said.
If confirmed, it would compound existing security risks for oil companies operating in Libya, a country awash with weapons and where militias often do as they please.
Libya said it was investigating the late night blast on a section of the pipeline linking Field 103, operated by the Zueitina Oil company, to the eastern terminal, which has a capacity of 60,000-70,000 barrels per day (bpd).
The explosion struck the light oil condensate section of the network, which was damaged more severely than the crude oil section. Pumping resumed relatively quickly, while repairs to the condensate pipeline, which took longer, have only just finished.
"The investigation is not completed yet but it looks like it was sabotage. The information gathered from those who have been to the site indicates this did not happen from inside the pipeline," a senior Libyan oil industry source said.
"If it was sabotage, this is not good for the country and the Libyan people. It underlines the importance of having a good protection system in place so this is not repeated elsewhere."
Libya's fast return to almost pre-war oil output levels of around 1.6 million bpd has been hurt by a wave of disruptions, mainly protests and strikes, that have briefly cut production.
There have been no reported cases of sabotage yet following the end of the 2011 war that ousted Muammar Gaddafi.
Two probes are being conducted into the incident: one by a committee of oil experts, and another by police from the town of Ajdabiyah, some 20 km (12 miles) from the blast site.
"This is a complex investigation and nothing can be disclosed at the moment. It should be concluded within a week," Ibrahim Balban, head of first committee said. A Zueitina spokesman in Tripoli said he was not aware of the probe details.
The pipeline also carries crude produced by the Abu Attifel field, which has a capacity of 70,000 bpd and is operated by the Mellitah Oil Company, a joint venture between the National Oil Corporation and Italy's Eni ; and oil from the smaller Nakhlah oil field, operated by Germany's Wintershall.
"Based on the information that we have and according to what experts have told us, this absolutely points to sabotage," a source familiar with the Ajdabiyah police probe said.
Libya has a 15,000-strong oil force guard, made up mainly of former rebel fighters. However still lacking proper training, the men have at times fought amongst themselves.
Last month violence erupted between rival factions of the force over who should control security at two eastern oilfields. This came after armed clashes at the Mellitah gas complex, which halted gas exports to Italy for several days.
"This blast could be linked to brigades trying to undermine each other for securing installations," another oil source said.
"If it's just positioning between militia groups, their interest will still be broadly aligned with keeping production flowing," Richard Mallinson of consultancy Energy Aspects said .
"The alternative would be an Islamist group but it does not quite line up with that," he added. "We've had one incident, we haven't seen any statements claiming responsibility."
Deputy Oil Minister Omar Shakmak said Libya aimed for an average 1.5 million bpd output this year and 1.7 million bpd from the third quarter.
In the light of past disruptions, Mallinson saw output struggling to exceed 1.3-1.4 million bpd this year: "If we introduce the new element, and had deliberate sabotage and attacks, we would be revising downwards those forecasts". (Writing by Marie-Louise Gumuchian. editing by William Hardy)