Oil workers strike over insecurity in Libya's Benghazi TRIPOLI (Reuters) - Oil workers, civil servants and private sector staff went on strike in the Libyan port city of Benghazi on Tuesday, protesting against deteriorating security a day after deadly clashes there between the army and Islamist militants. The mass walkout was the latest sign of growing anger against militias who helped oust Muammar Gaddafi two years go but have kept their weapons and regularly challenge the fragile new government and its security forces. There has been particular concern about mounting violence in Benghazi and the surrounding eastern region, the site of about 60 percent of Libya's oil production. Schools, universities and many shops and businesses also shut down at the start of the three-day strike. Organisers said they wanted all militias to leave Libya's second city. "Staff in the oil sector in Benghazi ... will join the civil obedience starting today," said Saad Fakhri, deputy head of Libya's union of oil workers. Administrative staff from Arabian Gulf Co and Ras Lanuf Oil and Gas Processing Company, both subsidies of state National Oil Corp (NOC), as well as other companies were taking part, he added. There was no immediate comment from the companies on the industrial action and what impact it might have on their work. At least nine people were killed on Monday during gun battles between the Libyan army and Islamist militants in Benghazi. Security officials said the militants were from Ansar al-Sharia, hardline Islamists blamed for last year's attack on the U.S. consulate in Benghazi in which the U.S. ambassador and three Americans were killed. Ansar al-Sharia fighters had left their base in Benghazi on Tuesday, but it was unclear where they had gone. Militias and former fighters had roamed unchallenged in the city where another armed group demanding autonomy has taken over vital ports and slashed Libyan oil shipments for months. Militiamen clashed with crowds mounting similar protests against instability in Tripoli earlier this month, leaving more than 40 people dead. The militias later pulled out of the capital, leaving the army to control its streets. Libya's troops, many of them still in training, and its central government, have struggled to contain rival militias and former fighters who have often clashed in territorial disputes and personal feuds. Western powers are keen to help Prime Minister Ali Zeidan rebuild the military. But analysts say its efforts are sometimes hampered by links between militias and some political leaders. Reporting by Ghaith Shennib; Writing by Ulf Laessing; editing by Patrick Markey and Andrew Heavens