Stock index futures pointed to a lower open on Monday as Chinese equities dropped sharply and commodities fell on concerns that asset prices have run ahead of the economic realities.

The Shanghai Composite Index <.SSEC> dived 6.7 percent to a three-month closing low and recorded its second-biggest monthly loss in 15 years on worries that corporate earnings failed to justify stock valuations.

Recent falls in China equities have caused jitters in stock markets around the world as some investors say prices are too high after a strong run-up. The S&P 500 index <.SPX> is up around 50 percent since a hitting a trough in early March.

I think that what we are facing here is a worried market ... we've had such a nice rise here that everyone is talking about pullback, said Peter Cardillo, chief market economist at Avalon Partners in New York. What is happening in the Chinese market is increasing that wall of worry.

Traders cited the sell-off in Chinese equities for a fall in the price of oil and other commodities. Oil dropped 2.4 percent, falling below $71 a barrel, and metal prices slid.

Financial shares also pulled back after a recent rally, led by a near 10 percent drop in American International Group Inc , as Barron's recommended investors take profits in Citigroup Inc . The Select Sector SPDR Financial ETF fell 1.7 percent.

In New York, shares in natural resource companies sold off before the bell. Exxon Mobil Corp dropped 0.6 percent to $69.77 while miner Freeport-McMoRan Copper & Gold Inc Inc fell 1.5 percent to $64.50.

S&P 500 futures fell 6.4 points and were below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures lost 73 points and Nasdaq 100 futures dropped 11.00 points.

In Japan, the Nikkei <.N225> average fell 0.4 percent while European shares <.FTEU3> also dipped 0.6 percent, although volume in Europe was light as the London market remained close for a holiday.

Oilfield service company Baker Hughes Inc said it will buy smaller competitor BJ Services Co for $5.5 billion in stock and cash, sending BJ's shares up 12.9 percent to $17.42 before the bell.

A regional survey on Monday is expected to show manufacturing in the U.S. Midwest improved again in August after last month posting its strongest gain since September. The report is the first in a busy week for economic data.

Economists in a Reuters poll forecast that the Chicago PMI index rose to 48 points in August from 43.4 points in July. The report is due at 9.45 a.m. (1345 GMT).

(Reporting by Edward Krudy; Editing by Padraic Cassidy)