(Adds percentage fall for the healthcare sector in paragraph 10)
* Healthcare stocks lead losses
* IQE tumbles after revenue warning; weighs on chip stocks
* German, French, eurozone PMIs better-than-expected
By Medha Singh and Susan Mathew
June 21 (Reuters) - European shares retreated on Friday, led by healthcare and media companies, at the end of a third week of gains dominated by signs that the world's big central banks are on the verge of another round of action to support growth.
Traders said many investors had been tempted to cash in some of this month's around 4% gain, encouraged by escalating tensions between Washington and Iran, and the pan-regional STOXX 600 index ended 0.4% lower.
It was also a day of "triple witching" where investors unwind positions in futures and options contracts before they expire which often leads to large unexpected moves in markets.
There was another jolt for chipmakers early in the day from British semiconductor wafer maker IQE Plc, warning of lower-than-expected revenue in 2019 as the U.S. ban on Huawei Technologies spreads through the industry's global supply chain.
The technology index fell 0.4%, and was among the biggest fallers.
Against that were German and French purchasing manager surveys which both topped expectations but were not enough to undo expectations that the European Central Bank and others will need to take action to support growth soon.
"Germany's manufacturing sector remains deep in contraction and the global economic outlook isn't great, so perhaps it's still a little early for optimism," said Craig Erlam, senior market analyst at Oanda in London.
The benchmark index, is on course to recover almost all of its losses from a sharp sell-off in May, as the Federal Reserve and ECB signalled that they were ready to act to counter the impact of U.S.-China trade tensions on a slowing global economy.
Investors will now look to a G20 summit in Japan next week for progress from the United States and China on resolving the differences that drove the worst monthly performance in European stock markets in more than two years in May.
Healthcare stocks led losses on the STOXX 600, down 1.4% after three days of gains when it added 3%.
Drugmaker Novartis fell 1.1% after a U.S. group that reviews the value of medicines said the list price for Swiss drugmaker's new multiple sclerosis drug Mayzent was "far out of line" compared with its benefits.
Paris-listed shares in SES also tumbled nearly 5% was the bigger faller on STOXX 600 on talks that the satellite communications firm could downgrade its second-quarter numbers.
A fall in the pound on growing expectations that hard Brexit proponent Boris Johnson will become prime minister kept Britain's FTSE 100 afloat, pushing up stocks in international companies who source much of their revenue abroad.
Dublin's ISEQ, which is sensitive to Brexit news, slipped 1.1%.
Markets in Finland and Sweden were shut for the Midsummer's Eve holiday.
Reporting by Amy Caren Daniel, Medha Singh and Susan Mathew in Bengaluru; editing by Patrick Graham, William Maclean