Federal officials and nuclear watchdogs have been working toward an agreement on environmental law concerns regarding the nation's plutonium pit production plan, but the process is taking longer than expected, a recent court filing says.

Both sides asked for a third extension of the deadline to complete the deal.

A federal judge ruled in September the National Nuclear Security Administration's decision to produce the radioactive cores of nuclear warheads at both Los Alamos National Laboratory and the Savannah River Site in South Carolina violated the National Environmental Policy Act. She tasked the federal government and advocacy groups with finding potential remedies.