U.S. Bank is suing the owners of One Riverfront Plaza in Westbrook over nonpayment of the property’s $20 million mortgage, asking the court to approve a foreclosure sale and appoint a receiver to take over management of the vacant office building.

The complaint, filed Aug. 11 by the Minneapolis-based bank in U.S. District Court for the District of Maine, alleges that One Riverfront’s owners have failed to make their mortgage payments on the property.

Five entities are listed as the property’s co-owners: Pendleton Westbrook SPE LLC; ZAK Westbrook SPE LLC; SRA Westbrook SPE LLC; SPC Westbrook SPE LLC; and Paris Westbrook SPE LLC. All five are based in Hackensack, New Jersey.

The six-story, 134,000-square-foot office building has been empty since January, when its sole tenant, insurer Disability RMS, relocated to South Portland.

U.S. Bank cited a number of reasons why it was asking the court to intervene. It noted that the property has been vacant for months, and that it is generating no operating revenue for maintenance and upkeep. The bank also said the building owners have a lease for up to 540 spaces in an adjacent parking garage, and that the loss of that lease would make the property unmarketable to prospective tenants.

U.S. Bank said the mortgage loan has been in default since January, when a balloon payment was due to pay off the loan in full.

Usually, when a commercial mortgage loan reaches its maturity date, the borrower refinances the loan and pays off the original lender. However, without a tenant in the building to generate revenue, it would be nearly impossible to obtain refinancing.

“As a result of Defendants’ breaches, Plaintiff has suffered and continues to suffer damages, including direct, incidental and consequential damages, attorneys’ fees and costs and interest accrued from the date of the Defendants’ default,” the complaint states.

U.S. Bank is asking the court to immediately appoint Portland-based Boulos Property Management as receiver of the property to take over all management and operations. It also requests that the court allow a foreclosure sale.

Finally, the bank is seeking damages including unpaid interest and legal fees. The property owners had not yet filed their response to the complaint as of Wednesday afternoon.

Disability RMS, a disability insurance provider and one of Westbrook’s largest employers, announced in September 2014 that it would relocate to South Portland when its lease at One Riverfront Plaza expired at the end of January. It employs about 350 workers.

City officials have said they are working together with the property owner to replace the office building’s sole occupant, but so far they have not signed any new tenants.