Russia said Monday it knew the proposed US missile defence shield was not aimed at its territory but still needed legal assurances that this would remain the case in the future.

Moscow formally demanded defence safeguards from Washington on May 3 after the United States reached an agreement to station anti-missile interceptors in Romania.

The United States argues that the shield is aimed at protecting Europe from missile attacks from countries such as Iran and would have no effect against Russia's vast nuclear arsenal.

But Moscow fears the shield could one day be deployed into a space-based weapon that could strike western and southern Russia.

Deputy Foreign Minister Sergei Ryabkov said Monday that the United States had informed it that it had no plans to provide the security safeguards Russia sought.

"We are disappointed with Washington's reaction," news agencies quoted the Russian diplomat as saying.

"We understand that the sides have no intention of developing their offensive strategic capabilities against each other," said Ryabkov.

"But we need safeguards that this is how things will remain in the future."

President Dmitry Medvedev stepped up the diplomatic pressure over the weekend by telling NATO heads of states in a letter that a European missile defence system could only be viable if Russia took part.

He and US President Barack Obama are set to meet on the sidelines of a Group of Eight leading industrialised nations' summit in France at the end of the month.