U.S. insurer and asset manager Principal Financial Group launched a bid on Thursday to buy Chilean pension company AFP Cuprum for $1.39 billion as part of an expansion drive in emerging markets.

Principal Financial agreed in October to use a public tender to buy Cuprum, including a 63 percent stake held by financial groups Empresas Penta and Inversiones Banpenta.

The U.S. insurer and asset manager offered 36,698.44 pesos for each of Cuprum's 17,996,300 shares, Principal Financial said in an advertisement in a local newspaper.

The success of the takeover bid, which starts December 28 and ends January 28, hinges on at least 63.44 percent of Cuprum's shares being sold to Principal Financial.

Chile's pension funds regulator has given the green light to the planned takeover of Cuprum, which has $32.7 billion in assets under management.

Cuprum shares were up 0.52 percent on the Santiago Stock Exchange at 39,000 in early trade on Thursday, outpacing the blue-chip IPSA's mild 0.05 percent increase.

Chile's private pension fund system has attracted investor attention due to high returns and robust local economic growth.

Medellin, Colombia-based Grupo Sura paid more than $3.5 billion last year for the regional assets of ING Groep NV , including Chilean pension fund AFP Capital.

($1 = 477 Chilean pesos)

(Reporting by Felipe Iturrieta and Anthony Esposito; editing by John Wallace)