JERUSALEM, Oct 17 (Reuters) - An Israeli commission investigating the storming of a Gaza-bound ship in which nine pro-Palestinian Turkish activists were killed issued an open invitation on Sunday for passengers and crew to testify.

A spokesman for the Turkel Commission said it had sent a letter to the Turkish embassy requesting help in building a list of prospective witnesses to the May 31 incident, which plunged ties between the former allies to an all-time low.

We are aware that there are issues which arise regarding arranging such testimony, and would be happy to work with the embassy and with the Turkish authorities ... to overcome any such obstacles, the spokesman quoted the letter as saying.

The panel appeared to be alluding to Israel's past vows to prosecute some of the hundreds of activists aboard the Mavi Marmara for their attempt to run the blockade of the Gaza Strip, an enclave ruled by Hamas Islamists, and their resistance to the boarding by Israeli naval marines.

Ankara has frowned upon what it sees as the Turkel Commission's limited mandate. The commission's findings, along with the results of an internal Israeli military inquiry, will be submitted to a separate investigation under U.N. Secretary-General Ban ki-Moon.

There was no immediate comment on the letter from the Turkish embassy, which the Turkel Commission previously asked to help locate the Mavi Marmara captain so he could be invited to testify. Nothing came of that effort, the panel spokesman said.