An IOC inspection team said the Chinese capital was making "considerable progress" after a visit on Thursday.
But it asked for more details on plans to improve air quality because of the smog that often hangs over the city.
"This is of the utmost importance to the athletes, who are the most important part of the Games," said IOC official Hein Verbruggen.
Verbruggen also said more work was needed to ease traffic flow on Beijing's notoriously congested streets.
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