PRAGUE, April 8 President Barack Obama and Russian President Dmitry Medvedev on Thursday signed the biggest nuclear arms pact in a generation, lacing the moment with new warnings of sanctions for Iran.

The treaty, sealed after months of halting negotiation, is significant not just for what it does but for what it symbolizes a fresh start for the United States and Russia, and evidence to a watching world that nuclear disarmament is more than a goal.

The pact commits their nations to slash the number of strategic nuclear warheads by one-third and more than halve the number of missiles, submarines and bombers carrying them.

That still leaves the two countries with enough nuclear firepower to ensure mutual destruction several times over, but the move sets a foundation for deeper reductions, which both sides are already pursuing.

“It sends a signal around the world that the United States and Russia are prepared to once again take leadership,” Obama said moments after he and Medvedev signed the treaty in a gleaming, ornate hall in the Czech Republics presidential castle.The Russian president said “The entire world community has won.”

The pact will shrink the limit of nuclear warheads to 1,550 per country over seven years, about a third less than the 2,200 currently permitted.

Looming over the celebration was Iran, which in the face of international pressures continues to say that its uranium enrichment programme is for peaceful purposes, not for weapons as suspected.

“We cannot turn a blind eye to this,” Medvedev said. But he said he was frank with Obama about how far Russia was willing to go, favouring only “smart” sanctions that might have hope of changing behaviour.

Russias Deputy Foreign Minister Sergei Ryabkov later elaborated by saying, for example, that Russia would not endorse a total embargo on the delivery of refined petroleum products into Iran.

The nuclear arms pact now faces a ratification vote in the Russian legislature and the US Senate. At home, Obamas team is struggling to get the necessary votes, and the president himself is directly involved. Obma said he was confident that Democrats and Republicans would see that the treaty protects US interests.

“I feel confident that we are going to be able to get it ratified,” Obama said.

But prospects of the treatys ratification are still uncertain. Democratic officials said they hoped the treaty could be ratified by the end of the year, but that the timing of the debate would depend upon the submission of technical documents accompanying the treaty.

Negotiations between the US and Russia got bogged down in disputes, including Russias objection to US missile defence plans for Europe. The Kremlin is still concerned about the plan but sought to tamp down talk it would withdraw from the new treaty if there is a buildup in the missile defence system. Russia codified its option to withdraw in a statement in connection with the treaty.

Obama said the treaty itself built trust that would help in solving any differences on the issue. Responded Medvedev “I am an optimist as well as my American colleague. I believe that we will be able to reach a compromise.”—AP