SINGAPORE, Jan 26 (Reuters) - London copper prices edged higher on Wednesday, in positive territory for the second session, ahead of U.S. Federal Open Market Committee's decision on interest rates.

Investors are awaiting the Fed's update to its policy plan, likely fleshing out timing on expected rate hikes and dwindling of its massive balance sheet.

Asian stock markets got off to a cautious start on Wednesday, after another volatile Wall Street session, as investors braced for the outcome of the Fed meeting.

* Three-month copper on the London Metal Exchange added 0.1 to $9,808.5 a tonne by 0438 GMT and the most-traded copper contract on the Shanghai Futures Exchange rose 0.5% to 70,160 yuan a tonne.

* Aluminium rose on worries over supply from major producer Russia because of the Ukraine crisis.

* Russia's Rusal is one of the world's biggest producers of aluminium and prices rocketed in 2018 to seven-year highs when the United States imposed sanctions on the company.

* Russia said on Tuesday that it was watching with great concern after the United States put 8,500 troops on alert to be ready to deploy to Europe in case of an escalation in the Ukraine crisis.

* Three-month aluminium on the London Metal Exchange (LME) added 0.8% to $3,117 a tonne.

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MARKETS NEWS

* Wall Street ended the day lower on Tuesday after another tumultuous day of trading, while oil jumped more than 2% as geopolitical tensions and Wednesday's Federal Reserve update occupied investor focus.

DATA/EVENTS (GMT) 1500 US New Home Sales-Units Dec 1900 US Federal Open Market Committee announces its decision on interest rates followed by statement

PRICES

Three month LME copper

Most active ShFE copper

Three month LME aluminium

Most active ShFE aluminium

Three month LME zinc

Most active ShFE zinc

Three month LME lead

Most active ShFE lead

Three month LME nickel

Most active ShFE nickel

Three month LME tin

Most active ShFE tin

ARBS (Reporting by Naveen Thukral; Editing by Shailesh Kuber)