The Soyuz TMA-15 craft carrying Belgian Frank de Winne, Canadian Robert Thirsk and Russian Roman Romanenko lifted off from the Russian-owned Baikonur cosmodrome in Kazakhstan as planned.

The men will join the three crew members already on board the ISS, giving the station six permanent members for the first time.

Thirsk called the expansion from a three-person to a six-person crew a "milestone" and said one of the mission goals was "to prove the station can support six people for a long period of time."

First European commander of ISS

The Soyuz TMA-15 spaceship is scheduled to dock with the ISS on Friday. The docking will mark the first time that all partners in the ISS - the US, Russia, Europe, Japan and Canada - will be represented on board at the same time.

In another first, Belgium's De Winne will become the first European commander to take over the ISS when the crew is rotated in October, before returning to Earth in November.

"What we'll do over the next months will be to prepare for future space exploration," De Winne told news agency AP.

A crowd of relatives, journalists and well-wishers, including Prince Philippe of Belgium, watched the spacecraft lift off into the hot afternoon skies over Kazakhstan's northern steppe.

Prince Philippe told reporters that the mission was "very important for Belgium."

The new crew will join Russian Gennady Padalka, US astronaut Michael Barratt and Japan's Koichi Wakata.

The ISS, which orbits 350 kilometers (220 miles) above Earth, is worth more than $100 billion.

Vladimir Solovyov, head of space programs for the Russian segment of ISS, told reporters that the expanded crew on the ISS will conduct technical and scientific experiments as well as medical tests.

sp/ap/afp/dpa

Editor: Susan Houlton