BOSTON (AP) — National Grid and labor union officials say they have been in “productive” negotiations for days but have not reached an agreement to end a monthslong lockout in Massachusetts.

The utility company and the United Steelworkers union said in a joint statement issued Saturday they were in talks all day Friday before National Grid presented the union with a revised offer at 11:30 p.m.

The two sides have agreed to schedule meetings for the union to formally respond to the latest offer, the details of which were not disclosed.

The company and the union have recently been signaling a breakthrough might be in sight. Both sides had hoped to end the six-month lockout by Dec. 28. National Grid also serves customers in Rhode Island and New York.