HELSINKI - Russia responded cautiously on Monday to U.S. President Barack Obama's plans for a nuclear-free world, saying a number of conditions would need to be met for the vision to become reality.

Obama pledged earlier this month in the Czech Republic to cut the U.S. nuclear arsenal, bring the Comprehensive Test Ban Treaty into force and seek tough penalties for those that broke rules on non-proliferation.

On the first day of a two-day official visit to Finland, Russian President Dmitry Medvedev said in a speech at Helsinki University that the topic of nuclear disarmament had become one of high hopes.

We noted what was said by the U.S. president in Prague that (disarmament) can be reached under a number of conditions, Medvedev said. These conditions are fair, but I would want to cite more conditions needed to achieve such a treaty.

Both Moscow and Washington see a chance to press the reset button on thorny relations driven to post-Cold War lows during the administration of Obama's predecessor George W. Bush.

Medvedev and Obama agreed at their first meeting in London this month to start joint work on a successor to the START-1 nuclear arms reduction treaty, which expires in December.

First talks on the new pact will begin in Rome later this month.

Medvedev said Moscow's conditions include:

-- a ban on deploying nuclear arms in space

-- making it impossible to compensate for a cut in nuclear arms by building up of conventional forces

-- making sure nuclear weapons are destroyed and not just stockpiled.

He repeated Russia's longstanding concern about U.S. plans for a missile shield in Poland and the Czech Republic, a plan promoted under the Bush administration and condemned by Moscow as an act of aggression aimed against it.

Bush had said the shield was needed to counter threats from rogue states, but Obama's administration has been less assertive in pushing the plan, saying it would be reviewed for cost-effectiveness and viability.

We are very concerned about the prospects of a unilateral deployment of anti-missile systems ... which complicates nuclear disarmament, Medvedev said.

Truly global anti-missile defense cannot match the interests of only one or several states. Its parameters cannot be set unilaterally, he said.

HELSINKI PLUS

Medvedev also repeated Russia's call for a new security pact to replace NATO, an idea that initially got a cool response when first broached at the Organization for Security and Cooperation in Europe's (OSCE) meeting in Helsinki in December.

Russia has said NATO is a Cold War relic. It wants a legally binding pact enshrining arms control, a commitment not to use force, and guarantees that no single state or group of states can take a dominant role in the continent's security.

Russia invites all European organizations to agree on comprehensive, modern and effective rules of the game, Medvedev said, referring to it as Helsinki plus, a reference to the 1975 Helsinki Accords that regulated Cold War security ties.

The start of such talks on a European security treaty could be given by a top summit with all Euro-Atlantic states, including the EU, NATO, OSCE ... regional organizations and states. We could there decide the best stage for talks and coordinate an agenda, he said.

He gave no timetable for when such a meeting could happen.

Medvedev noted that Russia had already cut troops and weaponry from its western outpost of Kaliningrad.

We decided to reduce the number of troops in the Kaliningrad region, and have already withdrawn many heavy weapons ... (and cut) our forces there many-fold, he said.