* Asia-Pacific shares ex-Japan down about 1 pct * Indonesian shares drop 1 pct * Singapore falls after 3 sessions of gains By Sumeet Gaikwad Sept 17 (Reuters) - Most Southeast Asian stock markets fell on Monday as reports of potential new U.S. tariffs on Chinese imports heightened investor worries over a protracted trade battle between the two countries. U.S. President Donald Trump is likely to announce new tariffs on about $200 billion on Chinese imports as early as Monday, a senior administration official told Reuters on Saturday. Trump's plan comes at a time when his Treasury Secretary Steven Mnuchin attempts to restart trade talks with another bilateral meeting this month. "This good cop bad cop routine continues to undermine Mnuchin's efforts as its still not clear if anyone other than Trump himself is commissioned to cut a deal. And not too unexpectedly and quite ominously China could cancel the meeting," said Stephen Innes, head of trading, APAC, at Oanda. MSCI's broadest index of Asia-Pacific shares outside Japan fell over 1 percent after three straight sessions of gains. Indonesian shares dropped about 1 percent, weighed down by consumer staples and financial stocks, ahead of the monthly trade balance data. The country's trade balance is expected to stay in the red in August although the size of the deficit may have narrowed, a Reuters poll showed on Friday. Consumer products maker Unilever Indonesia fell 1.8 percent, while Bank Mandiri was down over 3 percent. The index of the country's 45 most liquid stocks was down about 1.6 percent. Singapore shares dropped after three sessions of gains, with conglomerate Jardine Matheson Holdings Ltd down nearly 1 percent and lender United Overseas Bank falling 1.2 percent. Singapore's on-year non-oil domestic exports (NODX) growth slowed sharply in August as sales of pharmaceuticals came off the sizzling pace of the month before, official data showed on Monday. Philippine index was largely unchanged as losses in financials and telecom stocks offset gains in real estate stocks. Malaysian financial markets were shut for a holiday. For Asian Companies click; SOUTHEAST ASIAN STOCK MARKETS: AS AT 0348GMT Market Current Previous Close Pct Move Singapore 3139.71 3161.42 -0.69 Bangkok 1719.1 1722.21 -0.18 Manila 7419.18 7413.15 0.08 Jakarta 5866.387 5931.281 -1.09 Ho Chi Minh 990.32 991.34 -0.10 Change on year Market Current End 2017 Pct Move Singapore 3139.71 3402.92 -7.73 Bangkok 1719.1 1753.71 -1.97 Manila 7419.18 8558.42 -13.31 Jakarta 5866.387 6355.654 -7.70 Ho Chi Minh 990.32 984.24 0.62 (Reporting by Sumeet Gaikwad in Bengaluru; Editing by Amrutha Gayathri)