Turkey has refused to allow Israel to take part in a NATO summit next month because the Jewish state has not apologized for the 2010 killing of Turkish activists in a raid on a ship taking aid to Palestinians, a Turkish official said on Monday.

Relations between the regional powers deteriorated sharply after Israeli commandos raided the Mavi Marmara aid vessel in May 2010 to enforce a naval blockade of the Gaza Strip and killed nine Turks in clashes with activists.

Last September, Turkey expelled Israel's envoy and froze military cooperation after a UN report on the raid failed to prompt an apology from Israel.

"We did not give our consent on that issue," a Turkish official said when asked if Turkey was blocking Israel's participation in a NATO summit in Chicago on May 20-21.

He said Turkey was still seeking an official apology and compensation for the victims of the Mavi Marmara raid.

"NATO is an alliance and even though Israel is not a member its attendance means ... positive dialogue with NATO and all its members and without sorting this issue out we deem it not appropriate for Israel to be around," the official said.

Turkish media reported that some NATO members had sought Israel's participation in the summit as part of the alliance's partnership cooperation program, designed to strengthen relations with non-member countries.

Israel is a member of the Mediterranean Dialogue, a NATO outreach program, along with six other non-NATO countries.