(JTA) — The Turkish government of Prime Minister Recep Tayyip Erdogan divulged to Iran the identities of up to 10 Iranian spies for Israel who met with their Mossad handlers in Turkey, according to the Washington Post.

The newspaper’s opinion writer David Ignatius disclosed the incident, which he said occurred last year and is now being reported for the first time, in a column published Thursday.

He cited what he called knowledgeable sources as saying that the leak was a “significant” loss of intelligence and “an effort to slap the Israelis.”

Ignatius says the incident could explain why Israeli Prime Minister Benjamin Netanyahu was “so entrenched” in his refusal to meet Turkey’s demand of apologizing for the Mavi Marmara incident in which nine  Turkish citizens were killed when Israeli naval commandos boarded a ship attempting to break Israel’s naval blockade of the Gaza Strip.

Netanyahu spoke by phone to Erdogan in March, when he offered an American-brokered apology to the Turkish prime minister.

Ignatius said the United States did not protest the exposure of such a great intelligence loss to Turkish officials, choosing instead to continue to work on warming Turkish-American relations. He said that U.S. officials are not sure whether the intelligence exposure was in retaliation for the Gaza flotilla attack, or was just a sign of deteriorating relations between Turkey and Israel.

Israel, which Ignatius says has been cooperating with Turkish intelligence in secret for more than 50 years, does not trust Turkish intelligence chief Hakan Fidan, due to his ties with Iran, even as the United States deal with him on sensitive matters, according to Ignatius. He allegedly passed to Iran sensitive intelligence collected by the U.S. and Israel, the Wall Street Journal reported recently.