* Former FBI director to testify before Congress on Thursday
* UK election outcome, ECB meeting also on same day
* Oil falls further below $50 as Mideast rift weighs
* Indexes down: Dow 0.22 pct, S&P 0.24 pct, Nasdaq 0.20 pct (Updates to open)
By Tanya Agrawal
June 6 (Reuters) - U.S. stocks opened lower on Tuesday as investors shunned riskier assets ahead of what is expected to be a busy Thursday, when Britain goes to the polls and former FBI director James Comey testifies before Congress.
Comey, who was investigating alleged ties between President Donald Trump's 2016 campaign and Russia, was fired in May.
His testimony could dampen already flagging momentum for Trump's legislative agenda of rolling back healthcare reforms and overhauling the tax code.
Investors will also watch out for the European Central Bank's meet, where policymakers are expected to take a more benign view of the economy, according to sources.
"The indices are in a holding pattern, with a downside bias awaiting Thursday's key events, namely the Comey testimony, the ECB and GB elections," Peter Cardillo, chief market economist at First Standard Financial in New York, wrote in a note.
"On the other hand, investors abroad are rushing into Gold as the political situation in Great Britain and U.S. raises the level of 'Fear factor'."
Safe havens were in favor, with gold touching its highest in about seven weeks. Spot gold was up 0.96 percent at $1291.79 an ounce.
At 9:33 a.m. ET (1333 GMT), the Dow Jones Industrial Average was down 46.07 points, or 0.22 percent, at 21,137.97 and the S&P 500 was down 5.96 points, or 0.24 percent, at 2,430.14.
The Nasdaq Composite was down 12.43 points, or 0.2 percent, at 6,283.25.
Nine of the 11 major S&P 500 sectors were lower, with the financial index's 0.61 percent fall leading the decliners.
Oil prices fell further below $50 a barrel on concerns that a diplomatic rift between Qatar and several Arab states, including Saudi Arabia, could undermine efforts by OPEC to tighten the market.
Wall Street slipped on Monday as a drop in Apple partly offset gains in energy and financial stocks, some of the market's worst-performing sectors so far this year.
Still, stocks continue to hover around record levels, helped by a strong first-quarter corporate earnings season.
Shares of HD Supply Holdings were down 13.6 percent at $35.66 after the industrial distributor said it would sell a unit to private equity firm for $2.5 billion.
Thor Industries was up 10.4 percent at $104.15 after the RV maker's quarterly results beat expectations.
Michaels Cos fell 5.5 percent to $18.81 after the crafts and home decor retailer slashed its forecast.
Declining issues outnumbered advancers on the NYSE by 1,906 to 614. On the Nasdaq, 1,701 issues fell and 544 advanced.
The S&P 500 index showed 28 new 52-week highs and 11 new lows, while the Nasdaq recorded 82 new highs and 70 new lows. (Reporting by Tanya Agrawal in Bengaluru; Editing by Anil D'Silva)