(Combines stories, adds quotes, background)
By John O'Donnell
BRUSSELS, Sept 16 (Reuters) - The unilateral intervention of Japan to weaken its yen currency is not welcomed and the euro zone has told Japan that it disapproved of it, the chairman of euro zone finance ministers Jean-Claude Juncker said.
Juncker, who is also Luxembourg's prime minister, told reporters after a summit of EU leaders in Brussels that the Chinese yuan currency was still undervalued against the euro and that Europe had to insist more on this changing.
"The recent unilateral intervention at the initiative of the Japanese political and monetary authorities is not to be welcomed," Juncker said.
"We do think that the yen in relation to the euro is not overvalued but is still undervalued. We didn't like the way the Japanese authorities were dealing with that matter. We were discussing this yesterday and the day before with the Japanese, making it perfectly clear that we don't like the behaviour of the Japanese authorities," Juncker said.
He said interventions in markets were only fruitful if they were organised in a pre-committed way by the United States, the euro zone and by Japan.
Juncker stressed, however, that the Chinese renminbi currency, was also undervalued against the euro.
"We have to discuss more formally and with more insistence with our Chinese counterparts the elements related directly to foreign exchange rates. We do think that the yuan, the renminbi, is still undervalued," Juncker said.
"We think that we have good reasons to advocate, when discussing with our Chinese counterparts, that the Chinese monetary policy has to become more accomodative as far direct relations with the euro are concerned," he said.
"We have to explain to our Chinese counterparts that something has to change. The Chinese have taken over the last two or three months a different stand as far as monetary policy," Juncker said.
(Reporting by John O'Donnell, writing by Jan Strupczewski; Editing by Ron Askew)