raise its bid for rival tanker operator ICB Shipping AB, of Sweden, by 7.4 percent if ICB drops a plan to offer new shares to acquire Astro Tankers of Greece.

ICB is trying to block Frontline's bid by buying Astro Tankers from the Angelicoussis family of Greece for $309 million in stock and assumed debt, which would dilute Frontline's voting stake in ICB and leave the Greeks with 30 percent of ICB's voting shares.

Frontline said it will raise its offer to 125 kronor ($16.51) per Class B share, from 115 kronor, if ICB's board revokes its decision to acquire Astro no later than Friday, October 17. Frontline didn't change its offer of 130 kronor for each of the Class A shares, which carry more votes than the Class B shares.

It raised its offer for Class A shares from 115 kronor on October 1.

ICB's Class B shares were recently up 3.5 kronor, at 114.5, in Stockholm; Frontline fell 0.2 kroner, to 36.2, in Oslo.

"With only two days to go before ICB's shareholders' meeting, this is clearly a move ahead of a court case,'' said Cato Hellstenius, an analyst at Handelsbanken Markets. "Frontline is increasing the pressure from B-shareholders on ICB's management, which is very set on this deal.'' The bid for ICB comes as booming economies worldwide are boosting demand and rates for tanker space. Frontline, which currently controls 51.7 percent of ICB's capital and 31.4 percent of its votes, said last week it's considering suing ICB shareholders who vote in favor of the Astro Tankers transaction.

An increased bid will value ICB at $466 million, compared with the existing offer of $434 million.

While ICB's Class B shares have risen from 100 kronor since Frontline's first bid on September 1, the stock price is set to remain around today's price even if Frontline withdraws its offer, Hellstenius said.

"ICB is one of the cheapest tanker stocks around, and in the long term they may be able to increase the values more through the Astro cooperation,'' Hellstenius said. Still, "in the short term the Astro Tankers deal will dilute the shares, and they may also be hurt by lower liquidity.'' ICB's shares have outperformed Stockholm's General Index by 6.7 percent so far this year, while Frontline has beaten Oslo's OBX Total Index by 13.3 percent since it was listed on July 7.