Russian President Dmitry Medvedev said on Wednesday the world depended on the nuclear disarmament treaty he is due to sign with US President Barack Obama as he arrived in Prague for the ceremony.

"The treaty is an important document on which the overall situation in nuclear disarmament depends to a great extent -- and so does, speaking in general, the overall situation on the planet," Medvedev said after meeting Czech President Vaclav Klaus.

Medvedev landed in Prague on the eve of the landmark signature scheduled for Thursday at noon (1000 GMT) at the Prague Castle, the seat of the Czech presidency.

Obama is expected to land in Prague around 9:00 am (0700 GMT) on Thursday.

The two heads of state will sign a successor to the 1991 Strategic Arms Reduction Treaty (START), which expired last December, in the city where Obama called for a nuclear-free world in a keynote speech a year ago.

The deal slashes the number of deployed warheads by 30 percent from the levels set in the last major US-Russian disarmament treaty in 2002, specifying limits of 1,550 nuclear warheads for each of the two countries.

"That which will happen in Prague tomorrow will be a very important step in the process of disarmament and non-proliferation of weapons of mass destruction," Medvedev said.

He also thanked Klaus for his condolences following last week's attack on the Moscow underground, in which two female suicide bombers killed 40 people.

"It was a truly tragic event and the support from all over the world proves that the international community condemns acts of terror and similar crimes. It is important to feel we are united in this respect," said Medvedev.

"We will keep fighting against terrorism using all available means," he added.

The Russian president arrived in Prague from Bratislava, the capital of neighbouring Slovakia, where he commemorated the 65th anniversary of the city's World War II liberation.

He is scheduled to meet Obama and Klaus before the signature and leave for Moscow after a joint ceremonial lunch on Thursday afternoon.

Obama will meet 11 European leaders on Thursday evening, spend the night in Prague and leave around noon (1000 GMT) on Friday after bilateral talks with Czech leaders.