Asia's iron-ore futures tumbled on Monday, leading another bout of selling in the metals complex, after China's state planner warned against commodity price manipulation and vowed to clamp down on speculative trading.

The most-traded iron-ore contract for September delivery on China's Dalian Commodity Exchange ended daytime trading 5.2% lower at 1,064 yuan ($165.46) a tonne, after earlier hitting 1,016 yuan, its weakest since April 15.

Dalian iron-ore has plunged more than 20% since hitting a record high of 1,358 yuan on May 12, when tougher environmental restrictions on steel output in top producer China drove a rally in steel prices.

The most-liquid June contract for the steelmaking ingredient on the Singapore Exchange tumbled as much as 7.5% to $177.35 a tonne, its lowest since April 30.

The National Development and Reform Commission, China's top economic planner, along with other government agencies urged major domestic commodity companies not to drive up prices in a meeting on Sunday.

The talks followed a statement from China's cabinet on Wednesday that the government would manage "unreasonable" price increases for copper, coal, steel, and iron-ore.

"China's authorities continue to raise concerns about the rise of commodity prices, raising concerns that they may tighten regulations," ANZ commodity strategists said in a note.

Prices of steel products and other steel inputs also fell, with rebar on the Shanghai Futures Exchange down 3.6%, while hot-rolled coil slumped 3.9%.

Stainless steel shed 1.2%.

"As environmental regulations only work to increase steel prices in China, increasing profitability and thus production, the government is moving to take further action," Fitch Solutions said in a report.

Fitch believes the move "might blow the steam off steel's rally in the coming quarters starting with declines in Chinese steel prices seen in mid-May".

Dalian coking coal slipped just 0.2% as the selling pressure lost some steam, while coke dropped 1.7%.