Southeast Asian stock markets were sluggish in low-volume trade on Monday, in line with Asian peers as U.S. political uncertainties dampened hopes for quick passage of President Donald Trump's stimulus and tax reform agendas, weighing on investors' risk appetite.

The Trump administration, already dogged by investigations into alleged Russian meddling in the U.S. election, took a fresh hit on Friday after White House spokesman Sean Spicer resigned, highlighting an upheaval within the president's inner circle.

MSCI's broadest index of Asia-Pacific shares outside Japan was down 0.1 percent in early trade.

"Most Asian markets coming into this week are trading cautiously," said Victor Felix, an equity analyst with Manila-based AB Capital Securities.

Coupled with a shaky dollar, uncertainties surrounding Trump's administration have investors on edge, he added.   

The dollar index against a group of six currencies was little changed at 93.854, after touching 93.847, its lowest since June 2016.

In Southeast Asia, Singapore stocks fell as much as 0.6 percent ahead of inflation data due later in the day, with financials leading the decline. DBS Group Holdings, Oversea-Chinese Banking Corp and United Overseas Bank dropped 1 percent each.

The city-state's consumer price index (CPI) is expected to have risen 0.7 percent in June from a year earlier, a Reuters poll showed, slowing significantly from 1.4 percent in the previous month.

Philippine shares declined as much as 0.5 percent ahead of President Rodrigo Duterte's second State of the Nation Address. Heavyweights SM Prime Holdings and SM Investments Corp fell 2.6 percent and 1.8 percent, respectively.

Investors will be watching Duterte's address for clues on the tax reforms, how quickly his administration can roll out the big-ticket infrastructure programme they've been espousing the past year, and also how soon the conflict in Marawi can be ended, Felix said.

Vietnam shares declined as much as 1.1 percent to its lowest in nearly six weeks, and were headed for a third straight session of falls.

Saigon Beer Alcohol Beverage Corp was the biggest drag, falling as much as 4.9 percent.

Indonesian shares opened the session lower but recovered to trade marginally higher, helped by financials.

Thai stocks gained as much as 0.3 percent, while Malaysian shares were flat.