WASHINGTON: Defense lawyers are vowing to appeal the convictions of four former Blackwater security guards after a federal judge handed down lengthy prison terms for their roles in a 2007 shooting of unarmed civilians in Iraq.

Attorneys identified several issues Monday as likely forming the basis of an appeal, including vindictive prosecution and whether State Department contractors could be charged under a federal law that covers the overseas crimes of Defense Department civilian employees.

The move comes after US District Judge Royce Lamberth sentenced former guard Nicholas Slatten to life in prison and three others to 30-year terms for their roles in the shootings that killed 14 Iraqi civilians and wounded 17 others in Baghdad’s Nisoor Square. Slatten, who witnesses said was the first to fire shots in the melee, was sentenced to life after being convicted last October of first-degree murder. The three other guards — Paul Slough, Evan Liberty and Dustin Heard — were each sentenced to 30 years and one day in prison for charges that included manslaughter, attempted manslaughter and using firearms while committing a felony.

The incident strained US-Iraq relations and caused an international uproar over the use of private security guards in a war zone.

Lamberth announced the sentences after a daylong hearing at which defense lawyers had argued for leniency and presented character witnesses for their clients.