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Spot rupiah fell as much as 0.9 percent to 11,890 per dollar, its weakest since Feb. 14, on importers' dollar demand and its weakness in non-deliverable forwards markets.
The Singapore dollar fell to a near six-week low of 1.2587 to the greenback on slower growth in manufacturing activity in May.
It recovered some losses as it has a chart support area between 1.2585 and 1.2595, traders said.
The Philippine peso eased as interbank speculators covered bearish dollar bets.
Thailand's baht, however, edged up as foreign investors were net buyers of Bangkok shares in the previous two consecutive sessions on optimism over upcoming economic reforms by the military government.