Markets opened in the red on Monday morning, with investors left scratching their heads over fresh concerns in the upcoming U.S. presidential election while weak Japanese data and lower oil prices weighed on investor sentiment.

News broke on Friday that the Federal Bureau of Investigation (FBI) found new Hillary Clinton-related emails during a probe of devices used by former Congressman Anthony Weiner and his estranged wife, Clinton aide Huma Abedin. On Sunday, the FBI obtained a warrant to search the emails in relation to its investigation of the Democratic nominee's use of a private server for official emails while she served as secretary of state.

According to recent polls, the lead Clinton held over her Republican rival Donald Trump — who has hit the headlines for his controversial stance on immigration and allegations of sexual misconduct — shrank following the news, down from double digits last week. U.S. markets, buoyed initially by firmer third-quarter gross domestic product data, reversed from early gains to end lower.

This news spilled over into Europe, causing markets to begin the week trading lower. Oil markets were in the spotlight, as investors focused on the lack of concrete commitments by both Organization of Petroleum Exporting Countries (OPEC) and non-OPEC members on a planned production cut from their Friday and Saturday meetings.

OPEC countries seem far from reaching an agreement over an oil-supply cut. After more than 18 hours of talks in Vienna over the weekend, there was no tangible consensus from non-OPEC producers over joining the proposed production cut. Officials will be meeting at the end of November, hoping to have a final deal that boosts oil prices. However, the failed talks over the weekend sent prices on a downward trend during Asian trading. Brent was 0.5% lower at $49.46 a barrel and U.S. crude was down 0.39% at $48.51 a barrel.

Investors have some important events on their radar this week, including earnings from big companies such as Sony and Honda. Chinese and U.S. factory activity is scheduled for release on Tuesday while on Wednesday the Fed wraps up a scheduled two-day policy meeting. Strong third-quarter U.S. economic data released Friday has intensified expectations that policymakers will raise rates by the end of the year.

And as another month draws to a close, global equities have lost ground during the month of October. Mixed corporate earnings results meld with investor anxiety over the November 8th vote in the US and expectations that the Federal Reserve may hike interest rates before the year is out has had a negative impact on the markets, with investors finding it difficult to make their move.