Kilroy Realty Corp. on Monday said that its operating partnership, Kilroy Realty L.P., plans to offer senior unsecured notes in a private placement to institutional buyers.

The Los Angeles owner of office, industrial and multi-purpose properties said the notes will be guaranteed by Kilroy Realty Corp on a senior unsecured basis. The interest rate and other terms will be determined by negotiations among the parties.

The operating partnership intends to use net proceeds to repurchase all of its outstanding 3.250 percent exchangeable senior notes, due 2012, as part of a tender offer also announced Monday. The company will need $298 million plus accrued interest to do this, it said.

Shares were down 81 cents, or 2 percent, to $33.36 in midday trading on the Nasdaq.