Iraqi base@ (Adds Iraq military denial, changes dateline to Saturday)
TIKRIT, Iraq, June 22 (Reuters) - Iraqi and U.S. military spokesmen denied on Saturday U.S. forces were preparing to evacuate hundreds of staff of Lockheed Martin Corp and Sallyport Global from an Iraqi military base where they work as contractors.
Four separate military sources, who spoke to Reuters on condition of anonymity, said on Friday contractors from the two firms were getting ready to leave Balad military base, which hosts U.S. forces some 80 km (50 miles) north of Baghdad, over "potential security threats", without saying what those threats might be.
Iraqi and U.S. military spokesmen denied there were any such plans, which the sources disclosed at a time of rising regional tension between the United States and Iraq's neighbour Iran.
"There are no plans at this time to evacuate any personnel from Balad ... Should there be increased threats to our people, the U.S. Air Force will put measures in place to provide the protections required," Air Force Colonel Kevin Walker said in a statement.
Iraq's military spokesman said Iraq "protects the safety of our fighters and American advisers and trainers".
Three mortar shells hit the sprawling Balad base last week in an attack that caused no casualties, the military said. No one has claimed responsibility for the attack.
That incident was followed by attacks on two other military installations hosting U.S. forces, near Baghdad and in the northern city of Mosul.
U.S. energy giant ExxonMobil evacuated at least 21 foreign staff from a site near the southern city of Basra on Wednesday after a rocket also hit that facility, an Iraqi security source said.
One of the sources, a military official with knowledge of the base's daily operations had said that the U.S. military had informed Iraqi officials they would begin evacuating about half of the 800 employees who work for both companies at Balad.
The official said the evacuation would take about 10 days.
Two other military sources said the evacuation would take place in two stages and would be carried out by military aircraft.
The sources said the evacuation could start at any moment.
"Americans informed us that they will only keep limited, necessary staff who work closely on the maintenance of Iraqi F-16 war planes," one of the Iraqi sources said.
Lockheed Martin began delivering the first F-16s to Iraq in 2014.
A spokeswoman for Lockheed in the Middle East said: "We are not evacuating Lockheed Martin employees right now from Balad Air Base." She did not say whether any other evacuation was being prepared.
Local officials blamed Iran-backed Shi'ite militias for the Basra incident. Iran has not commented on the Iraq incidents but has strongly rejected accusations by Washington that it was behind several attacks on oil tankers in the Gulf in recent weeks.
The U.S. Embassy in Baghdad evacuated hundreds of staff last month after Washington cited unspecified threats from Iran to U.S. interests in the region. ExxonMobil evacuated its own staff last month, and had begun returning them to Iraq before the Basra attack.
Washington has ramped up sanctions pressure on Tehran since last year and several violent incidents in the Gulf have been blamed on the rising tension.
President Donald Trump on Friday said he had called off a U.S. strike on Iran at the last minute.
In Iraq, Iran backs several Shi'ite Muslim militias which have positions close to U.S. military installations.
Those militias have not publicly commented on the recent incidents.
Sunni militant group Islamic State is also trying to stage a comeback in Iraq and has mostly used hit-and-run insurgency tactics against Iraqi forces in recent months.
(Reporting by Ghazwan Hassan and Ahmed Rasheed in Baghdad; Writing by John Davison; Editing by Leslie Adler, Cynthia Osterman and Alison Williams)