New documents allegedly reveal that contrary to official claims by US government officials, the National Security Agency (NSA) has collected raw data from American citizens.
That data is then routinely shared with Israel's intelligence agency, SIGINT National Unit (ISNU), according to a memorandum of understanding between the Americans and Israeli spy agencies.
The documents come from former NSA analyst Edward Snowden who is now living in temporary asylum in Russia.
The data is not vetted by US analysts before being handed over to Israel.
The raw data could contain information about phone calls, email and other data of American citizens.
The 2009 memo is said to go through procedures how Israel must protect the constitutional rights of American citizens.
It stresses that those rights must be respected by Israeli intelligence staff. That said, it allows Israel to keep data on American citizens for up to a year.
Though the five-page document stresses that Israelis must comply with US law, there is no stated legal obligations to do so.
It also states that if Israeli intelligence comes across communications by US government officials, it must destroy them immediately.
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After the allegations were reported by the Guardian, the NSA wrote in a statement: "Whenever we share intelligence information, we comply with all applicable rules, including the rules to protect U.S. person information."
The open relationship on intelligence seems to belie earlier documents, which show the US considers Israel a target for counter-intelligence operations.
Israel is neither included in the so-called "Five Eyes" countries, which include Australia, Canada, UK, New Zealand - countries that are given more access to US intelligence information.
The American Civil Liberties Union told the Los Angeles Times that the new revelations should be troubling for all Americans.
"You can imagine a scenario in which somebody tries to get on a plane and is told by some foreign airline, 'We have you on a list,'" said Jameel Jaffer, deputy legal director of the American Civil Liberties Union.