Hang Seng Index futures opened the day session down 0.36% at 25,361, trading 203 points below the cash index.

The Trump administration has stepped up economic pressure on Iran and is threatening military strikes, former US ambassador to Tunisia Joey R. Hood said in an interview. Hood said Trump "is clearly aware of the limits of military strikes" but warned sanctions will not suddenly change Tehran's behavior. He noted it took two years of US sanctions to bring Iran to the negotiating table and produce the 2015 nuclear deal. Hood added the current environment differs: Washington has fewer allied partners and Tehran views US aims as "regime change", making a 2015-style outcome unlikely.

US Dallas Fed manufacturing shipments index rose to 14.1 in August from 8.8 previously.