Federal Reserve Bank of Atlanta President Dennis Lockhart said the central bank shouldn’t rule out asset purchases beyond the $600 billion planned by June because turmoil in the Middle East may cause an economic slowdown in the United States, Bloomberg Businessweek reported.

“With the information I have today, my first inclination is to be very cautious about extending asset purchases after June,” Lockhart said today in a speech. “Given the emergence of new risks, however, I prefer a posture of flexibility as regards policy options.”

Though the U.S. economy can absorb a “moderate increase” in oil prices, a bigger increase sustained over a longer period could do damage, Lockhart said. Research shows a “high correlation” between oil price shocks and recessions, he said.

Lockhart’s comments echoed Federal Reserve Chairman Ben Bernanke, who told Congress last week that economic conditions continue to justify holding the central bank’s target rate at near zero as well as additional monetary stimulus. Private economists are projecting the Federal Reserve will start to raise interest rates by early 2012 as the economy strengthens.

A third round of large-scale asset purchases could be needed in the event of another downturn, Lockhart said.