New plans have been filed for a 40-story development in the West End, blocks away from TD Garden and North Station.

Newton-based The RMR Group filed a letter of intent for a 600K SF project consisting of 420 residential units, a 300-room hotel and 30K SF of ground floor retail, restaurant and amenity space at 251 Causeway St., according to documents filed Wednesday with the Boston Planning Department.

"The Project will deliver much-needed housing, as well as hotel and retail uses and public realm improvements that will activate Causeway, North Washington and Medford Streets," RMR wrote in its letter of intent.

The firm said it plans to submit a project notification form in the second half of September.

“Filing our Letter of Intent is the first step in what we expect will be a robust public conversation for this reimagined project," RMR Vice President of Development Jesse Abair wrote in a statement to Bisnow. "We look forward to engaging with many different stakeholders in several neighborhoods to arrive at a shared vision for this key gateway location.”

The site consists of three adjacent parcels: two office buildings totaling 143K SF and 56K SF, and a six-unit apartment building. RMR wrote that the office buildings are mostly empty and efforts to retenant them "have not been successful," leading the group to file the redevelopment plans.

Former tenants included the Massachusetts Department of Agriculture Resources, the Massachusetts Fish & Game Department and the Veteran's Affairs Boston Clinic.

The proposed tower was first discussed in 2022, but formal plans were never filed by the group, Banker & Tradesman reported last September. Last year, RMR spearheaded efforts to rezone the Bulfinch Triangle to bring taller buildings and more housing, the Boston Business Journal reported.

UPDATE, AUG. 29, 5:20 P.M. ET: This story has been updated with a statement from RMR.