BRUSSELS, June 25 - Russia must take "concrete" steps to resolve the Ukraine crisis, US Secretary of State John Kerry said Wednesday, warning Moscow could easily reinstate its parliamentary approval for military intervention, AFP reported.

Russian President Vladimir Putin must publicly call for pro-Moscow rebels to lay down their arms and cut support to them, Kerry said, adding: "There are many concrete things that would make a difference on the ground."

Washington was "delighted" with Putin's decision, approved by parliament Wednesday, to revoke the blanket authorization to intervene if ethnic Russians in eastern Ukraine were threatened.

"It is an important, a great step -- but it can be reversed in 10 minutes," Kerry said.

A senior Russian lawmaker said the revocation should be seen as an act of goodwill to help facilitate peace efforts in Ukraine, where Moscow sees itself as the defender of the rights of the large Russian-speaking minority. But he said the authority could be reinstated at short notice.

"The President of the Russian Federation has enough means under the constitution and federal law to effectively influence the situation in Ukraine," Reuters reported citing Viktor Ozerov, head of the Federation Council's security committee.

"If, to that end, the president needs to take measures of a military nature, the Federation Council's Defense and Security Committee is ready ... to swiftly consider such a motion from the president. But I hope that will not be required."

Meanwhile, Kerry said that the shooting down of a Ukrainian helicopter, with the loss of nine lives Tuesday, was possible because the rebels had Russian weapons. He repeated his call for Moscow to cut the flow of arms and fighters into eastern Ukraine.

Putin's failure to come up with real commitments on the ground in the "next days and weeks," runs the risk of tougher sanctions, Kerry warned after a NATO foreign ministers meeting, stressing that preparations for such measures were ongoing.

Many ministers made a similar point, arguing that Russia must unambiguously sign up to the Ukraine government's peace plan or face the consequences.
Russia meanwhile said it hoped Kiev and the international community would take heed of the "positive signals" it was sending over the Ukraine crisis, including the withdrawal of the military intervention authorization.

"We are counting on the positive signals that the Russian president is now sending being heard across the world and, above all, in Ukraine," Deputy Foreign Minister Grigory Karasin told Russian news agencies. (afp/rt/ez)