* Raises bid to equivalent of 185 mln NOK from 171 mln

* New SBB bid on the cards, while Balder has raised stake

* Entra is Norway's biggest listed real estate firm

STOCKHOLM, Dec 18 (Reuters) - Real estate firm Castellum raised its bid for Norway's Entra by 14% on Friday, further escalating a Swedish battle over the future of the Oslo-listed peer.

Castellum in November launched a 30.8 billion Norwegian crown ($3.58 billion) cash and shares takeover bid for Entra, topping an offer from rival Swedish firm SBB.

On Friday Castellum said it was now offering eight newly issued Castellum shares for every 13 shares in Entra and 54.39 Norwegian crowns in cash per share in Entra. The revised offer values an Entra share at 185 Norwegian crowns per share.

"We are increasing our bid by 13.9%," Castellum said in a statement.

As an alternative to that revised offer, Castellum is also offering eligible Entra shareholders a so-called mix & match facility, it said in a statement.

The move comes after SBB, having last week withdrawn its offer of 165 Norwegian crowns per share, said on Wednesday that it had asked Entra for additional information as it was seeking to return to the negotiating table.

Swedish rival Balder meanwhile said on Thursday it had raised its stake in Entra to 15% from 10%. Balder, which made its first investment in the Norwegian firm on Dec. 7, has said it does not plan a full takeover.

Castellum also said on Friday it had agreed to sell a property portfolio to Blackstone Group for 18.1 billion Swedish crowns ($2.18 billion) net.

($1 = 8.6027 Norwegian crowns)

($1 = 8.2927 Swedish crowns) (Reporting by Anna Ringstrom; editing by Colm Fulton and Susan Fenton)