"We should have completed construction by 2010, but unfortunately we will only manage it by 2015," Energia President Vitaly Lopota said.
He said as a result Russia will request that foreign partners extend the life span of the ISS by five years to 2020.
He said this issue was dependent on funding. "Let us turn to Russian Finance Minister Alexei Kudrin with a question via the press - will Russian space programs and the construction of the Russian ISS segment continue?"
Alexei Krasnov, the head of the Federal Space Agency's department for manned flights, said Energia is to roll out four manned Soyuz spacecraft in 2009. "Perhaps we will build a fifth craft to give other countries who haven't been in space a chance to fulfill their dream, but everything depends on funding," he added.
The first ISS element, the Russian Zarya module, was put into orbit in November 1998. Several modules have been attached to the structure since then, but ongoing construction has missed the initial deadline, largely due to delays in U.S. shuttle launches following the disintegration of Columbia in 2003.
Upon its completion, the ISS will weigh 470 tons and be 109 meters long, 88.4 meters wide. Its total cost is expected to be $40 billion.