Russia's spacecraft producer Energiya will not provide any more Soyuz vessels for trips to the International Space Station unless funds could urgently be found, Energiya's president and general constructor warned Friday.

"We have vessels and funding for them for the next two trips, but I do not know what will happen with expeditions after that," Vitaly Lopota told reporters as quoted by the RIA Novosti news agency.

"We have no funds to produce new Soyuz craft. Unless we are granted loans or advance payment in the next two or three weeks, we cannot be responsible for future Soyuz production," Lopota explained.

The Soyuz is Russia's workhorse spacecraft that has carried out more than 1,600 flights, despite glitches that have bedevilled recent landings of the Soyuz capsule.

An April 19 landing, where the capsule entered the atmosphere at an unusually steep angle, subjecting astronauts to uncomfortably strong G forces and landing 420 kilometres (260 miles) from its target, as well as a similar October 2007 incident, raised doubts about the Soyuz's safety.

However, Friday's landing of the Soyuz carrying US space tourist Richard Garriott and Russian cosmonauts Sergei Volkov and Oleg Kononenko, went smoothly as scheduled.

NASA will be totally reliant on the Soyuz for transporting astronauts and cargo to the ISS after its space shuttle fleet retires in 2010 and until the shuttle's successor vehicle is ready, expected in 2015 at the earliest.