Dutch mail firm PostNL NV said it raised the value of its stake in TNT Express, the delivery firm which US peer United Parcel Service has offered to buy, reflecting gains in the share price. PostNL owns nearly a third of TNT Express, which underperformed for much of last year, prompting activist shareholders to agitate for a shakeup and pushing up the share price towards the end of 2011. UPS made a 4.9 billion euro ($6.60 billion) takeover offer for TNT earlier this month, which the Dutch firm turned down, but the two parties are still talking, pushing the stock to trade above the 9 euro per share offer. PostNL said in a statement on Monday that its stake in TNT Express was valued at 936 million euros at the end of 2011. “The share price of TNT Express increased during the last quarter of 2011, leading to a partial reversal of 98 million euro of the previous impairment,” PostNL said as it announced fourth-quarter earnings. PostNL said last year it had taken impairments of more than 700 million euros on its TNT stake as its shares more than halved in value from May, when TNT was spun off from PostNL, to early October.TNT’s share price has surged more than 60 per cent since the end of 2011, raising the market value of PostNL’s stake to about 1.5 billion euros. Chief Executive Harry Koorstra declined to comment on continuing talks with UPS, which offered 4.9 billion euros in cash on Feb.17, or whether any other buyer such as FedEx had approached with a rival offer. He previously indicated a buyout could be supported by the PostNL board. Two other substantial investors in TNT Express, US-based Jana Partners and Canadian group Alberta Investment Management Corporation (AIMCO), which had pushed for a turnaround in its performance, both reduced their stakes last week after TNT shares rallied nearly 40 per cent in response to the UPS offer. Jana Partners cut its stake in the Dutch delivery company to 4.49 per cent from 7.15 per cent, while AIMCO cut its stake to 4.59 per cent from 7.52 per cent, according to a filing with the Dutch financial market regulator AFM.