Russia's timetable for manned flights to the moon has been pushed back two more years with no launches until 2018, the head of Russia's space agency said.

Roscosmos chief Vladimir Popovkin said the project will not meet its initial projected flight date of 2015-16, RIA Novosti reported.

The new piloted spacecraft is intended to replace the aging Soyuz craft on voyages to the International Space Station and beyond.

"We are thinking of higher [compared to the International Space Station] orbits, and flights to the moon, and developing the technology to fly to Mars," Popovkin said. "So we are developing a future system, first of all of course the pressurized, launchable module."

The six-seat ship could be adapted for a variety of missions, "maybe just long automated missions, or moon missions, or to a space station between Earth and the moon, or beyond the moon," he said.

It would, however, "not immediately be a reusable system," Popovkin said.

Developing a reusable craft depends "primarily on thermal-protective coatings, and we have different approaches to solving that issue," he said.

First, he said, work would have to be carried out to test whether the module is safe for "re-entry to Earth ... at twice space speeds, which is a completely different stress."