* Rates unchanged
* To taper bond purchases from Sept
* To end bond buys at year-end
* Rates steady at least until next summer (Updates euro fall, fresh quotes)
RIGA/FRANKFURT, June 14 (Reuters) - The European Central Bank announced on Thursday it would wrap up its unprecedented bond purchase scheme by the close of the year, its biggest step in dismantling crisis-era stimulus a decade after the start of the euro zone's economic downturn.
But in a balanced announcement reflecting the uncertainties hanging over the region's economy, it also signaled the move would not mean a rapid policy tightening by adding that interest rates would stay at record lows "at least through the summer of 2019 and in any case for as long as necessary."
The new rates guidance prompted the euro to reverse initial gains to fall over one percent to $1.1670, close to its biggest one-day loss since October. Markets had been anticipating a 10-basis-point hike in the ECB's benchmark deposit rate -- currently at -0.4 percent -- by June 2019.
ECB President Mario Draghi declined to give more detail about the timing of rate moves in a news conference after the policy meeting, this time held away from the bank's Frankfurt headquarters in the Latvian capital Riga.
"We didn't discuss when to raise rates," he said.
"This decision has been taken in the presence of a strong economy with increasing uncertainty," he said of a political landscape characterized notably by rising trade tensions between the United States, Europe and China.
The ECB also downgraded its euro zone growth forecast for this year to 2.1 percent from 2.4 percent previously, while upgrading its inflation forecast to 1.7 percent from 1.4 percent, largely as a result of rising oil prices.
"This is a very fine balance -- a bit more hawkish on QE, but rather dovish on rates -- that Mario Draghi hopes will keep the markets on an even keel and avoid a taper tantrum," said Neil Wilson, chief market analyst for Markets.com.
Though full policy normalization will take years, investors are already braced for the end of easy money from the world's central banks. A hawkish U.S. Federal Reserve dropped a crisis-era stimulus pledge on Wednesday while the ECB had already begun rolling back support after a five-year run of economic growth.
The ECB said the monthly pace of its net asset purchases would be halved to 15 billion euros from September until the end of December 2018, at which point purchases would end.
By putting a specific end-date on its stimulus, the ECB is taking a more decisive step than when the U.S. Federal Reserve started its own taper in December 2013. Then, it did not commit to a specific end or any subsequent steps.
The biggest complication could be a murky economic outlook, muddied by the developing trade war, a populist challenge from Italy's new government and softening export demand.
But ECB policymakers have long argued that their mandate is to bring inflation back to target, not to prop up growth or fight off market turbulence in any particular country.
Italian bond yields rose sharply this month as a new government of anti-establishment parties promised higher spending. That threatens a clash with Brussels, which is pushing Rome to cut the euro zone's second-biggest debt pile.
A broader slowdown could make it harder for the ECB to cut support if lower growth eases pressure on inflation, a threat to the bank's credibility as it has missed its inflation target of almost 2 percent for over five years.
While inflation has remained weak, higher oil prices, increasingly evident wage pressures and record employment suggest that prices will be moving up in the coming years, even if more slowly than the ECB had originally hoped.
ECB Chief Economist Peter Praet, a Draghi ally and one of the most dovish members of the rate-setting Governing Council, recently argued that progress has been made on the inflation criteria, a strong hint that stimulus would be pared back.
The euro's 5 percent fall against the dollar since April is also helping the ECB as the weaker currency is increasing the cost of imports and boosting inflation. While a rebound is likely, the U.S. Fed's tightening stance will limit the potential for a big rise in the euro.
($1 = 0.8490 euros)
(Writing by Mark John; Editing by Catherine Evans)