Already, top Fed officials have defended their view that the U.S. central bank should probably raise interest rates soon, saying they still intended to keep the economy running fast enough to boost employment and inflation.

Recent strong readings on the U.S. labor market, and signs that inflation was finally beginning to pick up, is encouraging some policymakers to believe that rates should be hiked, if not as soon as September's policy meeting then at least before the end of the year.

Traders currently put chances of a December rate hike at about 42 percent.

Vietnam shares  .VNI were up as much as 1.4 percent after index heavyweight Vietcombank  VCB.HM gained as much as 6.5 percent to its highest since July 14 after it said it would pay a 10 pct cash dividend and 35 pct share dividend to shareholders.

The index has gained 13.7 percent this year as of Thursday's close.

Philippine shares  .PSI fell 0.6 percent, with telecom stocks leading the losers. PLDT Inc  TEL.PS lost nearly 1 percent, and Globe Telecom Inc  GLO.PS was down 2.1 percent.

Investors continue to take a cautious stance ahead of Janet Yellen's speech, looking for indications of a rate hike, SB Equities said in a note, adding that "trading participants have increased chatter on a potential surprise in tonight's speech."

Thai shares  .SETI were up 0.6 percent, led by technology and basic materials, while Singapore  .STI and Indonesia were down marginally.

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SOUTHEAST ASIAN STOCK MARKETS

STOCK MARKETS

Change at 0455 GMT

Market              

Current       

Prev close   

Pct Move

 Singapore           

2868.52       

2876.93      

-0.29

 Bangkok             

1553.58       

1544.1       

0.61

 Manila              

7804.35       

7854.54      

-0.64

 Jakarta             

5435.869      

5454.116     

-0.33

 Kuala Lumpur        

1681.91       

1680.3       

0.10

 Ho Chi Minh         

666.33        

658.5        

1.19

Current       

End 2015     

Pct Move

 Singapore           

2868.52       

2882.73      

-0.49

 Bangkok             

1553.58       

1288.02      

20.62

 Manila              

7804.35       

6952.08      

12.26

 Jakarta             

5435.869      

4593.008     

18.35

 Kuala Lumpur        

1681.91       

1692.51      

-0.63

 Ho Chi Minh         

666.33        

579.03       

15.08