The owners of Two Liberty Place have put the office portion of the Center City tower up for sale, according to CBRE executive vice president Robert Fahey, who is handling the listing.

Florida-based Parkway Properties is selling the office space in the 57-story tower to focus on its core portfolio of assets in the southeastern United States, Fahey said Tuesday.

He said a significant amount of interest during the week in which the property has been marketed has come from overseas buyers who are newly discovering Philadelphia as a target for investment.

"There is significant international demand for these low-volatility, low-risk office assets in major metropolitan areas," Fahey said.

The upper residential floors are separately owned, and not part of the listing.

Two Liberty, designed by architect Helmut Jahn, opened in 1990 as the corporate headquarters of Cigna, which occupied the entire 1.2 million-square-foot structure.

After Cigna reduced its occupancy in 2005, the building's top 20 floors were converted to luxury condominiums, and other tenants joined the insurer in its offices.

Parkway Properties, a publicly traded real estate trust, acquired Two Liberty's offices as part of a 2011 merger. The company was positioned to exit the Philadelphia market with the property's sale after Cigna renewed a lease there in August, executive vice president M. Jayson Lipsey said in a statement at the time.

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