(Updates after U.S. market open, Changes byline, previous dateline LONDON)
* U.S. dollar falls, oil falls
* U.S. stocks fail to hold gains, turn negative
* Asian stock markets: https://tmsnrt.rs/2zpUAr4
* For Reuters Live Markets blog on European and U.s. stock markets please click on:
NEW YORK, Jan 23 (Reuters) - A global index of stock markets turned negative on Wednesday as worries over U.S. politics, global economic growth and trade tensions offset a boost from quarterly earnings reports. The U.S. dollar and oil prices also declined.
U.S. Treasury yields climbed but analysts expect the $15.6 trillion market to be confined within a tight trading range due to a dearth of incentives from fresh economic data amid the longest-ever U.S. government shutdown.
The U.S. dollar failed to maintain small gains from earlier in the session as uncertainties kept investors on the sidelines and the yen fell after the Bank of Japan kept its stimulus program in place.
"The trade conflicts and tensions, the (U.S. government) shutdown and certainly more chatter about global growth in 2019, those are the factors that need to be hashed out before we get a clear direction," said Minh Trang, senior currency trader at Silicon Valley Bank in Santa Clara, California.
After falling more than 1 percent a day ago, Wall Street's three major equity indexes erased earlier gains to turn negative. Strong quarterly reports from Procter & Gamble, Comcast Corp and International Business Machines offered some support.
But U.S. political uncertainty weighed heavily on investors.
White House economic adviser Kevin Hassett said in a CNN interview the United States could see zero growth in the first three months if the partial government shutdown is extended for the whole quarter.
"It's another kick in the shins for investors to be concerned about," said Chad Morganlander, senior portfolio manager at Washington Crossing Advisors in Florham Park, New Jersey.
The Dow Jones Industrial Average fell 74.9 points, or 0.31 percent, to 24,329.58, the S&P 500 lost 18.54 points, or 0.70 percent, to 2,614.36 and the Nasdaq Composite dropped 62.11 points, or 0.88 percent, to 6,958.24.
MSCI's gauge of stocks across the globe shed 0.21 percent, while the pan-European STOXX 600 index lost 0.06 percent. shed 0.42
Some weak results from European companies, including luxury goods brand Burberry and Ingenico, damped confidence about the fourth quarter in Europe.
"If earnings come in reasonably around expectations, the reality is equities are attractively valued across global regions," said James Bateman, chief investment officer of multi asset at Fidelity International.
"If they disappoint consistently there is going to be a real reappraisal of fair value."
Investors kept a close eye on China on hopes more stimulus measures to shore up its economy would ease worries over slow progress in trade talks between Washington and Beijing.
U.S. President Donald Trump said he would not soften his position that Beijing must make real structural reforms, including how it handles intellectual property, to reach a trade deal, advisers said.
The dollar index, tracking the greenback against six major peers, fell 0.25 percent, with the euro up 0.27 percent to $1.1389.
The Japanese yen weakened 0.07 percent versus the greenback to 109.46 per dollar.
Benchmark 10-year notes last fell 2/32 in price to yield 2.7391 percent, from 2.732 percent late on Tuesday.
Oil prices sank, following U.S. stocks down, on concerns about global economic weakness, forecasts for record U.S. shale production and lower U.S. gasoline prices.
U.S. crude fell 1.79 percent to $52.06 per barrel. (Additional reporting by Saqib Iqbal Ahmed, April Joyner, Richard Leong and Lewis Krauskopf in New York, Josephine Mason, Sujata Rao and Helen Reid in LONDON. Hideyuki Sano and Shinichi Saoshiro in TOKYO Editing by Bernadette Baum)