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Space exploration remains a priority for Russia, President Dmitry Medvedev has said, as the country marks the 50th anniversary of the first human space flight by cosmonaut Yuri Gagarin.

"We were first into space, we have a huge number of achievements, we don't want to lose our advantage," he said.

The event was marked by ceremonies and a 50-gun salute in Moscow.

Gagarin's achievement dispelled fears humans could not survive beyond the Earth's atmosphere.

Since his flight in 1961, more than 500 men and women have followed in his footsteps.

In a video link-up with the crew of the International Space Station as part of the events marking the anniversary, Mr Medvedev said Russia would continue to devote resources to space exploration.

"Humanity will continue to invest in space. I want to say, in the name of Russia, that we will of course do this as space is a priority for us," he added.

Later, at an award ceremony in the Kremlin, President Medvedev told former cosmonauts and Gagarin's widow Valentina that Gagarin's flight was "the greatest triumph of our country" at the time.

Before Gagarin, no-one knew for sure if a human could withstand the conditions in space, says the ´óÏó´«Ã½'s Steve Rosenberg in Moscow; some believed weightlessness would induce madness, that the G-forces on take off and re-entry would crush the body, and there was concern over the effects of radiation.

But when Gagarin's face and voice were beamed down from space, the world saw that the cosmos was not to be feared - it was to be explored, our correspondent says.

On 12 April 1961, to the cry of "Let's go!", Yuri Gagarin embarked on a voyage lasting 108 minutes in a tiny two-metre-wide (6ft) capsule, then ejected and parachuted down into a field in central Russia.

"The most emotional moment was when we heard he was walking and waving; his arms and legs were whole. We understood in one sigh that our five to six years of hard work had paid off and we had achieved something huge," said veteran cosmonaut Georgy Grechko, now 79, who worked as an engineer on Gagarin's space capsule.

The US responded 10 months later, when John Glenn made the first US orbital flight.

Unlike in Gagarin's time, space is no longer the preserve of two superpowers, our correspondent adds.

Today as well as Russia and America, there are other players in space, including Europe, China and India - with their own programmes and their own vision for space exploration.