* S&P and Nasdaq post 6th straight quarter of gains
* MSCI's global index, European shares post quarterly gains
* Oil prices decline as fears of Iraqi violence retreat
* Yen at five-week high versus dollar (Adds close of U.S. markets)
By Herbert Lash
NEW YORK, June 30 (Reuters) - Global stock markets posted a fourth straight quarter of gains on Monday, aided by the loose monetary policies of major central banks that have helped drive risk appetite, while concerns about the world's economic health have underpinned government debt.
Stocks on Wall Street closed mixed, but the S&P 500 and Nasdaq Composite indexes closed a sixth straight quarter of gains - a streak not seen since the euphoria over technology shares came to a halt in 2000.
MSCI's all-country index, which tracks shares in 45 countries, rose 0.18 percent. It gained more than 4 percent in the second quarter, aided by the prospect that monetary policy in the major economies will remain accommodative for longer, and it posted a fourth straight quarter of gains.
In Europe, the FTSEurofirst 300 index of top regional shares also posted a fourth straight quarter of gains, though for the day it finished down 0.05 percent to end the quarter at 1,370.60.
Major stock indexes have rallied this year, and the S&P 500 has posted more than 20 record closing highs, even as the U.S. Federal Reserve trims its economic stimulus.
"The Fed and other global monetary forces have done their best to keep this market as liquid as possible, and that liquidity is restricting investors from finding a place other than stocks and have enabled risk takers to stay confident," said Rick Meckler, president of investment firm LibertyView Capital Management in Jersey City, New Jersey.
Bond yields, which had been expected to rise after a run-up late last year, have broadly fallen. Barclays' Aggregate U.S. bond index is up 3.82 percent in the first half of the year as benchmark yields have fallen nearly half a percentage point.
The 10-year Treasury note rose 1/32 in price to yield 2.5268 percent.
The Dow Jones industrial average fell 25.24 points, or 0.15 percent, to close at 16,826.6. The S&P 500 lost 0.73 point, or 0.04 percent, to 1,960.23 and the Nasdaq Composite added 10.248 points, or 0.23 percent, to 4,408.178.
For the quarter, the Dow rose 2.2 percent, the S&P 500 was up 4.7 percent and the Nasdaq gained 5.0 percent. All three indexes also rose for the month of June.
A sense of complacency in markets drew the attention of the Bank for International Settlements, a forum of the world's top central banks, which warned on Sunday that markets were increasingly out of sync with shaky global growth prospects.
Several early warning indicators signal vulnerabilities have been building in the financial systems of several countries, it said.
Gold was steady near a two-month high, poised to set a second straight quarterly gain after political tensions bolstered demand.
U.S. COMEX gold futures for August delivery settled up $2 at $1,322 an ounce.
The dollar remained under pressure, awaiting this week's busy calendar of U.S. data, which includes the June non-farm payrolls report on Thursday, a day earlier than usual due to the U.S. Independence Day holiday on Friday.
The dollar fell versus the yen to a six-week low of 101.21 yen, and was last at 101.32, down 0.04 percent.
The euro rose to an almost six-week high of $1.3697 and last changed hands at $1.3694, up 0.34 percent.
Brent crude oil dropped below $113 a barrel as fears of a disruption to oil output from Iraq receded after government forces launched a pushback against a Sunni militant insurgency.
Brent was down 94 cents to settle at $112.36 a barrel. U.S. crude lost 37 cents to settle at $105.37 a barrel.
(Reporting by Herbert Lash; Additional reporting by Anirban Nag in London; Editing by Dan Grebler and Leslie Adler)