Nov 9(Reuters) - Spain's real estate group Inmobiliaria Colonial on Thursday posted a net attributable loss of 299 million euros ($320 million) for the first nine months of the year, hit by a drop in the value of its assets.

The company had reported a net profit of 398 million euros in the year-earlier period.

Central banks' tightening monetary policy has put the real estate sector in troubles since the second half of last year, slowing down investments in properties.

With sovereign debt offering higher returns due to high interest rates, investors are demanding higher returns on real estate assets, driving down their values.

However, the group reported a 8% rise in its operating performance from January to September compared to one year ago.

Asked about the difference between the attributable net loss and the recurring net profit, CEO said that European real estate investment companies such as Colonial and its peer Merlin Properties have to include the impact of an updated valuation of their properties.

Colonial's third-quarter results do not include an updated valuation of its assets, which is presented every six months and dropped 3% at the end of the second quarter from the previous reading, leading the company to incur losses.

The nine-month results take into account the assets valuation decrease until the end of June.

"We will have to wait for the asset repricing process to be over. We will see more (by the end of the year)", Colonial CEO Pere Viñolas told reporters in a conference call. ($1 = 0.9337 euros) (Reporting by Matteo Allievi and Jakub Olesiuk; editing by David Evans)