Nasa is planning to launch a Mars probe this summer

The announcement came after talks in Moscow between the heads of the two agencies, Nasa administrator Sean O'Keefe and his Russian counterpart Yuri Koptev, about the International Space Station (ISS).

Heads from the 16-nation group involved in building the ISS are to meet in September to decide on future development of the project.

The issue of greater American funding for the space station was not discussed at the Moscow meeting, but the Russian space agency, Rosaviakosmos, is to receive a greater share of the existing budget.

Russia and the US "have agreed to begin joint exploration of Mars and carry out joint unmanned interplanetary station flight programmes," Sergei Gorbunov, Rosaviakosmos spokesman, said.

"In addition, it was decided that Russia can take part in US space tenders," Mr Gorbunov added.

Funding problems

Nasa is currently reliant on Russia to continue ferrying crews back and forth to the ISS after the agency grounded its entire shuttle fleet following the loss of the Columbia orbiter on 1 February.

The ISS was put in jeopardy by the shuttle disaster

However, the Russian space agency is already hard-pressed financially and although it has been given a budget increase to cover the next six months, it says it will be unable to meet its commitments next year without American help.

Mr Gorbunov said the issue of additional US funding was not even broached at the meeting.

Nonetheless, Mr O'Keefe and Mr Koptev have given the green light to a programme to build a US-Russian space probe for the exploration of Mars.

One senior Russian space agency official told Russian news agency Itar-Tass that a similar joint project was started 10 years ago.

Vasily Moroz from the Russian Space Research Centre said the two sides had considered using a US-built probe with a Russian booster rocket and descent module, but that the project was drawn to a halt by funding issues.

The Moscow talks coincided with the deployment of a Soyuz craft to ferry a new crew to the ISS. The existing crew - two Americans and a Russian - had a dramatic re-entry that took their craft more than 400 kilometres (250 miles) beyond its intended landing site.