UPDATE 3-Turkey's Yildirim buys stake in Gemport from Isbank

* Deal reached after drawn-out negotiations

* Stake valued at $350-400 mln - analyst

* Port is Turkey's 10th biggest

* Yildirim says working on another port deal

(Adds comments from Yildirim Holding CFO)

By Birsen Altayli and Nevzat Devranoglu

ISTANBUL, Oct 2 (Reuters) - Turkish industrial group Yildirim Holding will invest further in the country's fast-growing ports industry after buying a majority stake in Isbank's port unit Gemlik Liman (Gemport), its finance director said on Tuesday.

Yildirim's Yilport unit has agreed to buy the 54 percent stake, Gemport said in a statement, giving no financial details.

"In the next two and a half months we are going to finalise the acquisition of Gemport," Yildirim Holdings' chief financial officer Evren Ozturk told Reuters.

"After this deal we're going to buy another port which we are still negotiating. Following these two deals, the ports portfolio of Yildirim Holding will far exceed $2 billion from $1.5 billion now."

Analysts at Oyak Securities estimated the Gemport stake was worth $350 million-$400 million.

Sources familiar with the matter said Yildirim had out-bid Turkish army pension fund Oyak in a close contest.

"The decision was not made until the last minute after eleventh-hour negotiations," one of the sources said.

Gemport is located near Istanbul, south-east of the Marmara Sea, and has an annual container storage capacity of 600,000 20-foot equivalent units (TEU), according to its website. TEU is a standard unit for the cargo capacity of container ships and container terminals.

Gemport was the 10th biggest port in Turkey in terms of handling capacity as of 2009, according to an Ernst and Young report.

Yildirim Holding was founded in 1963 and is active in mining, ports, construction, ship building and fertilizers.

Turkey has a coastline of more than 8,000 km and is strategically positioned between Europe and Asia. The country has around 175 ports, mostly privately operated and concentrated around Istanbul, its largest city.

Turkey does 88 percent of its trade via its ports, according to Ernst and Young. Its overall handling capacity was 6.6 million TEU in 2011, three times that of Greece, according to independent market monitor Drewry Shipping Consultants.

(Additional reporting by Nevzat Devranoglu; Writing by Seda Sezer; Editing by Nick Tattersall and Elaine Hardcastle)

(seda.sezer@thomsonreuters.com; +90 212 350 7051; Reuters Messaging: seda.sezer@thomsonreuters.com)