NEW YORK (REUTERS) - US 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.

Mr 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 US raises the level of 'Fear factor'."

Safe havens were in favour, with gold touching its highest in about seven weeks. Spot gold was up 0.96 per cent at US$1291.79 an ounce.

At 9:33 a.m. ET (9:33 p.m. Singapore time), the Dow Jones Industrial Average was down 46.07 points, or 0.22 per cent, at 21,137.97 and the S&P 500 was down 5.96 points, or 0.24 per cent, at 2,430.14. The Nasdaq Composite was down 12.43 points, or 0.2 per cent, at 6,283.25. Nine of the 11 major S&P 500 sectors were lower, with the financial index's 0.61 per cent fall leading the decliners.

Oil prices fell further below US$50 (S$69) 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.