Asian shares stumbled and the U.S. dollar was on the defensive on Wednesday as signs that Republican U.S. presidential candidate Donald Trump could be closing the gap with his Democratic rival Hillary Clinton spooked investors.

A man walks past at an electronic board showing the Japanese yen's exchange rate against British pound (R) and Euro outside a brokerage in Tokyo, Japan, July 6, 2016.

Anxiety in markets has deepened over a possible Trump victory given uncertainty on the Republican candidate's stance on several issues including foreign policy, trade relations and immigrants, while Clinton is viewed as a candidate of the status quo.

MSCI's broadest index of Asia-Pacific shares outside Japan .MIAPJ0000PUS dropped 0.4 percent while Japan's Nikkei .N225 fell 1.1 percent.

The tumultuous presidential race appeared to tighten after news that the Federal Bureau of Investigation was reviewing more emails as part of a probe into Clinton's use of a private email server.

While Clinton held a five-percentage-point lead over Trump, according to a Reuters/Ipsos opinion poll released on Monday, some other polls showed her Republican rival ahead by 1-2 percentage points.

That pushed U.S. S&P 500 Index .SPX down to a four-month closing low on Tuesday. The CBOE volatility index .VIX, often seen as investors' fear gauge, briefly rose to a two-month high above 20 percent.

In the currency market, traders sold the dollar partly as they suspect Trump would prefer a weaker dollar given his protectionist stance on international trade.

The euro EUR= rose to a three-week high of $1.1069, up about two percent from its 7-1/2-month low of $1.0851 hit just over a week ago. Against the yen, the dollar slipped to 104.03 yen JPY= from three-month high of 105.54 yen set on Friday.

"If you had a long dollar position on the view that the dollar would gain because Clinton would win, you would surely close that position because her victory is less certain," said Koichi Yoshikawa, executive director of financial markets at Standard Chartered Bank.

"And people were buying back the euro because that is the currency that had been being shorted the most against the dollar," he added.

Other safe-haven assets were also favoured, with the Swiss franc rising to 1.0782 franc per euro EURCHF=, its highest level since late June. Gold XAU= hit a four-week high of $1,291.6 per ounce on Tuesday and last stood at $1,288.5.

In contrast, the Mexican peso MXN=D2, seen as the most vulnerable to a Trump presidency due to his proposals such as building a wall along the U.S. border with Mexico, posted its biggest fall in two months.

The peso slid to 19.265 to the dollar, its lowest level since early October.

The tense back drop in markets came as the Federal Reserve holds its two-day policy meeting, with its statement due later on Wednesday.

While traders do not expect the central bank to raise interest rates just a week ahead of the presidential election, they are looking for signs that the Fed is set to hike rates in December.

U.S. interest rate futures <0#FF:> are pricing in about 70 percent chance of a rate hike in December but virtually no likelihood of a hike on Wednesday.

Oil prices tumbled to one-month lows as a trade group's report of larger-than-expected U.S. crude inventory added to concerns about oversupply from growing doubts over whether oil producing countries can agree on an output cut later this month.

Brent crude futures LCOc1 fell to $47.90 per barrel, having hit a low of $47.72 on Tuesday.

Still, even as investors were moving out of riskier assets, copper CMCU3 bucked the trend, rising to a three-month high of $4,922 a tonne.

Source: Reuters