LONDON (AFP) -- A secret memo proves that the Israeli government knew that its occupation of Palestinian land was illegal after it won the Six Day War in 1967, a British newspaper reported Saturday.

Theodor Meron, who wrote the memo as the Israeli foreign ministry's legal advisor at the time, said "I believe I would have given the same opinion today," according to The Independent newspaper.

With Israel now celebrating the 40th anniversary of the war, the 76-year-old Meron, who went on to become a leading international jurist, challenges Israel's long-held argument that settlements do not violate international law. The Independent said it obtained a copy of his legal opinion, which was marked "Top Secret" and "Extremely Urgent." Quoting its author, the newspaper said the memo concluded "that civilian settlement in the administered territories contravenes the explicit provisions of the Fourth Geneva Convention."

Meron also told the newspaper that then foreign minister Abba Eban was "sympathetic" to his view that civilian settlement would go against the Hague and Geneva conventions governing the conduct of occupying powers.

But the Labour government at the time progressively approved the settlements in the captured West Bank despite the secret legal opinion which had been passed on to then prime minister Levi Eshkol.

Such actions paved the way for at least 240,000 Israelis to settle in the the West Bank.

Meron, who served as president of the International Criminal Tribunal for the former Yugoslavia until 2005, was also quoted as telling the Independent that the settlements have proven to be a real stumbling block.

"It's obvious to me that the fact that settlements were established and the pace of the establishment of the settlements made peacemaking much more difficult," he was quoted as saying.

In the Six Day War in June 1967, Israel captured the Sinai peninsula from Egypt, the Golan Heights from Syria and the West Bank and East Beit-ul-Moqaddas from Jordan.