Obama and Medvedev cut nuclear arsenals, warn Iran
US President Barack Obama and Russian leader Dmitry Medvedev signed a landmark treaty Thursday committing to major nuclear arms cuts, while also warning Iran to expect sanctions over its nuclear drive.

The treaty was signed in a key year for anti-proliferation efforts with the international community struggling to persuade North Korea to disarm and to counter Iran's nuclear drive.

The two presidents warned Iran to expect sanctions if it maintains its refusal to halt uranium enrichment and cooperate with UN atomic watchdog inspectors amid Western suspicions that it is seeking a bomb.

Obama called for "smart" and "strong" sanctions by the United Nations, which in May will hold a review conference on the nuclear Non-Proliferation Treaty (NPT).

Medvedev said: "Unfortunately Tehran is not reacting to an array of constructive compromise proposals. We cannot close our eyes to this."

"I have said many times that sanctions very often do not work, but sometimes they are necessary... These need to be smart sanctions, capable of prompting the right behaviour," Medvedev said.

US to 'ratchet up' Iran pressure over nuclear plans
In an hour-long phone call with Chinese President Hu Jintao , Obama had stressed "the importance of working together to ensure that Iran lives up to its international obligations", the White House said.

International sanctions would not prevent Iran from pursuing its nuclear activities, he said.

Chinese officials have not commented after the talks.

China's foreign minister has said he still hopes the nuclear issue can be resolved through negotiations. However, the US ambassador to the UN, Susan Rice, said China had indicated it was ready to hold "serious" talks with Western powers on a new UN resolution.

UN Sanction
Envoys from Russia, Britain, China, France, and the United States -- the five veto-holding members of the UN Security Council -- plus Germany met on April 8 in New York to discuss a possible fourth round of sanctions against Tehran for failing to halt uranium enrichment activities that the United States and its allies fear could be diverted toward production of a nuclear weapon.

Obama Administration Unveils New Nuclear Weapons Policy
The Obama administration unveiled a new nuclear weapons policy that is meant to narrow the circumstances in which the U.S. would use nuclear weapons as well as address a variety of other issues dealing with nuclear weapons.

Under the new policy the U.S. will not use or threaten to use nuclear weapons against non-nuclear weapons states that are party to the Nuclear Non-Proliferation Treaty. These states must also be in compliance with their nuclear nonproliferation obligations.

In addition, the U.S. would only consider the use of nuclear weapons in extreme circumstances to defend the interests of the U.S. or its allies and partners.

How about Israel?
Israel's Prime Minister called off his trip to Washington  to attend a conference on the spread of nuclear weapons, officials in his office said, fearing Israel would be singled out over its own nuclear program.

Benjamin Netanyahu had said he would attend the conference to underline the dangers of terrorists acquiring nuclear weapons, but suddenly called off the trip less than two days after he announced he would take part.

Officials in his office said early Friday that Netanyahu reversed himself because some nations planned to use the conference to target Israel over its barely concealed nuclear weapons program. The officials spoke on condition of anonymity because no announcement has been made.