Image courtesy of BioMed Realty

BioMed Realty has completed its $163 million acquisition of a development site in Somerville’s expanding Assembly Square commercial cluster, with plans for 1.3 million square feet of office, lab and retail space.

Sellers Cresset Group and Novaya Real Estate Ventures began permitting for the Xmbly site, located just south and west of Federal Realty’s Assembly Row, before agreeing to sell it to BioMed last year.

The first phase of the project will be a 420,000-square-foot office-lab building on Middlesex Avenue, a BioMed executive said last fall. The plans were amended last year by Somerville officials to eliminate a 167-unit apartment tower previously approved for the master-planned site, while adding 100,000 square feet of lab space.

“Thriving mini-clusters in highly desirable and centrally located places like Somerville help ensure our members can thrive and bring new therapies and cures to patients faster, Kendalle Burlin O’Connell, president and COO of Cambridge-based industry organization MassBio, said in a statement.

The site contains an existing 162,000-square-foot office building and adjacent 7.5-acre site.

In December, BioMed paid $3.5 billion for a life science portfolio in East Cambridge and recently acquired the ground lease on the former John Hancock headquarters in Boston’s Seaport District.

According to industry sources, BioMed also has agreed to buy 321 Harrison Ave. and 1000 Washington St. in Boston’s South End, which contains an existing 242,000-square-foot office building and four-story parking garage, along with a speculative 235,000-square-foot office building currently under construction.