At 0508 GMT, no currency had changed for than about 0.3 percent against the dollar. Among decliners, the biggest was the Thai baht, while the largest gainer was the Indian rupee, which strengthened as oil prices dipped.

The US dollar strengthened on Monday as concerns of a global economic slowdown, heightened by weak economic data from China and Europe, trimmed appetites for riskier assets such as emerging Asian currencies.

Meanwhile, investors are cautious about the trajectory of US monetary policy as markets await the Fed's interest rate decision due early Thursday Asia time.

Saktiandi Supaat, head of FX research at Maybank (Singapore), said in a note to clients on Friday that a Fed hike "accompanied by a still-hawkish tone in the statement and press conference could power the USD and weigh on" Asian currencies other than the yen.

On the other hand, a "dovish hike" could allow Southeast Asian currencies to recover ahead of the Christmas holidays, he said.

On Monday, one regional loser was the Indonesian rupiah , which was down 0.2 percent, part of that on data showing November's trade deficit was the widest in over five years, as exports slumped.

The deficit was $2.05 billion, while a Reuters poll had expected a gap $830 million.

In India, government data on Friday showed the country's trade gap narrowed from the prior month. Lower oil prices have helped the world's third-biggest oil importer which buys over 80 percent of its crude oil from overseas.

The Philippine peso and the Singapore dollar were fractionally stronger against the dollar.

CHINESE YUAN

The yuan on Monday firmed 0.2 percent at 6.898 per dollar, edging away from the psychologically important benchmark of 7 to the dollar.

"The yuan was stronger this morning partly on the back of stronger than expected fixing," said Khoon Goh, head of Asia research at ANZ Banking Group (Singapore).

Investors awaited President Xi Jinping's speech at a conference marking the 40th anniversary of China's reform and opening up on Tuesday. The conferences comes at a time Chinese business executives and others to call for faster reforms.

The following table shows rates for Asian currencies against the dollar at 0508 GMT.