Norges Bank Investment Management has agreed to buy 45% stakes in three US office properties.

US REIT Boston Properties said it was selling the interests in 601 Lexington Avenue and Atlantic Wharf, in New York City, and 100 Federal Street in Boston for $1.5bn (€1.2bn).

Boston Properties is forming a joint venture with Norges Bank, which manages Norway’s sovereign wealth fund, to manage the assets, which total 3.7m sqft.

Two of the three properties are, Boston said, unencumbered by debt.

As reported in July, Norges Bank is in talks to buy two office buildings properties in Boston and San Francisco for $915m, according to sources.

The assets are being bought in a joint venture with US insurer MetLife and in a separate deal with TIAA-CREF.

Norges Bank and MetLife’s joint venture, split 47.5% and 52.5%, has invested $2.26bn since creation in December last year, with no target for future investment.

Norges Bank began increasing its exposure to real estate in early 2013, targeting office and retail properties in established markets. The mandate to invest in real estate was broadened from 1 January 2013 to include countries outside Europe – with the US first stop.

By the end of last year, investments for its real estate portfolio accounted for 1% of its fund.

A first property investment in the US was made at the start of 2013 via the $600m acquisition of a 49.9% stake in a five-asset portfolio in Boston, New York and Washington.