Israel's state-appointed inquiry into the lethal storming of a Gaza-bound aid flotilla in May is almost complete, the chief investigator said on Wednesday after one of his fellow panel members died.

Set up in hope of stemming international fury at Israeli marines' killing of nine Turkish pro-Palestinian activists aboard one of the ships, the Turkel Commission is also providing material for a separate inquest at the United Nations.

One of the five Israeli investigators, 93-year-old former ambassador Shabtai Rosenne, died of heart failure overnight but a spokesman said the commission's work would stay on schedule.

Interviewed on Israel's Army Radio, the panel chairman, retired Supreme Court justice Jacob Turkel, said he was undecided on whether to replace Rosenne.

Asked if the inquest was nearing completion, he said: "Yes, certainly. We have by now gathered most of the testimony ... If there will be more witnesses testifying, they will be witnesses of lesser importance, and not a large number of them remain."

Among those asked to appear before the commission is Mahmut Tural, captain of the converted cruise ship Mavi Marmara, where the activists were killed after the Israelis boarded it. Turkel said a response from Tural had yet to be received.

The Turkel Commission includes two foreign observers but has been criticised by the Turkish government for its limited scope. The Turks have demanded an apology and compensation from Israel, which has refused, saying its navy acted in self-defence.