The billionaire Jewish financier George Soros has secretly donated vast sums of money to the dovish American Israel lobby J Street, despite repeated denials by the organisation.

Hungarian-born Mr Soros, 80, has been regarded with suspicion by Zionist groups since he claimed in 2003 that Jews and Israel were to blame for rising antisemitism.

The businessman, worth more than $14bn, has always spoken of his support for J Street, which was created in 2008 as an alternative to the highly influential, Conservative lobby Aipac.

J Street bills itself as "pro-Israel, pro-peace", favours a negotiated two-state solution and is critical of the Netanyahu administration. An as-yet unnamed British group is also in the process of forming, based on the J Street model. However, J Street has repeatedly had its pro-Israel credentials questioned by elements in the Jewish community.

Its three-year long denial that it received donations from Mr Soros will have further shaken belief that it is truly pro-Israel. The group has opposed sanctions on Iran and called Operation Cast Lead "disproportionate".

Many wonder if J Street really is pro-Israel

When contacted by the JC in September, a spokeswoman for George Soros's Open Society Foundation also said no donations were made to J Street.

But the Washington Post revealed this week that tax forms from Mr Soros and his two children show they contributed $245,000 (£154,000) to J Street in 2008.

J Street's president Jeremy Ben-Ami later admitted the family contributed over a quarter of a million dollars per year over the past three years.

Until last week a statement on the organisation's website, under a section headed "Myths and Facts", said: "George Soros very publicly stated his decision not to be engaged in J Street when it was launched - precisely out of fear that his involvement would be used against the organisation.

"J Street's Executive Director has stated many times that he would in fact be very pleased to have funding from Mr Soros and the offer remains open to him to be a funder should he wish to support the effort."

The site has now been amended.

Mr Ben-Ami admitted J Street had been "misleading" with its statements and said he took personal responsibility for the backlash. But he added: "Those who attack J Street over the sources of its funding are not good government watchdogs concerned about the state of non-profit financing in the US.

"If our critics are really so concerned with transparency of funding, then I challenge them to reveal the sources of funds for the organisations with which they agree."

Mr Soros made his fortune as a currency speculator and investor, and is believed to have made around £1bn from the Black Wednesday crisis in 1992.

He has donated a large percentage of his personal fortune to left-wing groups including Human Rights Watch.