* China's top planner said to be investigating surge in futures
* Shanghai rebar, Dalian iron ore posts 4th monthly gain in 5
* Spot iron ore on course for fifth monthly increase
By Manolo Serapio Jr
MANILA, Feb 28 (Reuters) - Chinese steel and iron ore futures fell nearly 3 percent on Tuesday after sharp gains in the prior session amid reports that the country's top economic planner was investigating the recent surge in futures markets.
China's National Development and Reform Commission (NDRC) this month questioned futures brokers on whether speculation has distorted commodity futures prices amid concerns that the recent rally will drive inflation higher, Bloomberg reported on Monday, citing people with knowledge of the matter.
The NDRC is tasked with overseeing the Chinese economy, regulating prices and approving major infrastructure projects.
The most-active rebar on the Shanghai Futures Exchange closed down 2.9 percent at 3,471 yuan a tonne after touching a three-year high of 3,648 yuan on Monday. The construction steel product has gained nearly 7 percent this month.
Iron ore on the Dalian Commodity Exchange dropped 2.8 percent to end at 690.50 yuan per tonne. The steelmaking raw material hit a record high of 741.50 yuan last week and has risen 9 percent this month.
February marked the fourth monthly gain out of five for both commodities.
Wang Di from CRU consultancy in Beijing said the price decline may have been due to the reported probe into futures markets. But she said prices remain strong.
"It just seems that the current steel price is very high and enables steelmakers to have really high margin. But it's still a question mark after the NPC meeting whether there's downstream demand that will support this," said Di.
Di was referring to China's National People's Congress which begins its annual meeting on Friday.
Weaker futures could pull down spot iron ore prices once more after recovering some lost ground on Monday, when iron ore for delivery to China's Qingdao port .IO62-CNO=MB rose 2 percent to $92.33 a tonne, according to Metal Bulletin.
The spot benchmark has risen almost 11 percent in February, on track for a fifth straight monthly gain.
Stockpiles of imported iron ore at 46 major Chinese ports reached 129.35 million tonnes last week, the highest since 2004 when SteelHome consultancy began tracking the data. SH-TOT-IRONINV
Reporting by Manolo Serapio Jr.; Editing by Biju Dwarakanath