TORONTO -- North American stock markets fell and the price of oil dropped Friday after the FBI announced it will investigate new emails connected to Democratic U.S. presidential candidate Hillary Clinton's private server.

FBI Director James B. Comey revealed the emails' existence in a letter to Congress, saying the agency will review them to determine if they contain classified information. The FBI said in July its criminal investigation had been completed.

"It has been the single biggest driver of the market today," said Scott Vali, vice-president of equities at CIBC Asset Management.

"(The) market doesn't like uncertainty and this creates more uncertainty."

He said the markets started to drop shortly after the news emerged, leading to speculation about the outcome of the U.S. presidential election that takes place on Nov. 8.

People had started to become comfortable with the idea that Clinton would win the presidency, said Vali.

Her opponent, Republican candidate Donald Trump, is viewed as negative for several reasons, including trade and the economy, he said.

In Toronto, the S&P/TSX composite index fell 48.46 points to 14,785.29.

South of the border, the Dow Jones industrial average shed 8.49 points to 18,161.19, while the S&P 500 dropped by 6.63 points to 2,126.41. The Nasdaq composite lost 25.87 points to 5,190.10.

Vali said the price of gold jumped as the markets sold off, with the December gold contract gaining $7.30 to US$1,276.80 an ounce.

The FBI report about new emails tied to Clinton also dragged down the price of oil as the December crude oil contract plummeted by $1.02 to US$48.70 per barrel.

That added to a five-day drop of US$2.15 -- the biggest weekly decrease in the price of oil in six weeks. In the week ending Sept. 16, oil prices fell US$2.85.

Friday's decline in the price of oil came mostly from the renewed possibility of a Trump victory, but an ongoing OPEC meeting had "limited" impact as well, said Vali.

The representatives from the 14 member nations of the Organization of the Petroleum Exporting Countries met in Vienna Friday to continue discussions regarding a preliminary agreement to cut oil production reached last month in Algiers. The group plans to meet with some non-OPEC members to discuss these matters Saturday.

Full details of the deal will be released after the group meets again in Vienna at the end of November.

The commodity-sensitive loonie inched up 0.02 of a U.S. cent to 74.72 cents US.

Elsewhere in commodities, December natural gas rose 3.7 cents to about US$3.11 per mmBTU and December copper contracts were up three cents at US$2.19 a pound.