Barack Obama and Vladimir Putin clashed over the Crimea referendum during a telephone call on Sunday, as the US president dismissed claims from his Russian counterpart that the vote was legal and warned him that Moscow would be punished.

Obama rejected an argument from Putin that the vote, which Moscow claims overwhelmingly endorsed Crimean secession from Ukraine to become part of Russia, was “fully consistent with the norms of international law and the UN Charter”, according to the White House.



In a statement, it said: “President Obama emphasised that the Crimean ‘referendum’, which violates the Ukrainian constitution and occurred under duress of Russian military intervention, would never be recognised by the United States and the international community.”

Russian state media reported that 95.5% of people in the southern province, which has been occupied by Russian forces for the past fortnight, voted on Sunday in favour of leaving Ukraine. Some 3.5% were said to have chosen more autonomy while remaining part of the country.

A Kremlin statement said Putin also told Obama during the call, which the US initiated, that the case of Crimea was in line with the so-called “Kosovo precedent”. Putin has claimed that the recognition of the former Yugoslavian territory as a sovereign state in 2008 established a legal framework for secession that could be repeated by other separatist movements.



The White House’s read-out of the call did not mention such a discussion and instead said that Obama “emphasised that Russia’s actions were in violation of Ukraine’s sovereignty and territorial integrity”.

The US president was said to have complained to Putin that Russian military exercises on Ukraine’s eastern border “only exacerbate the tension” and warned him that the US and allies were “prepared to impose additional costs on Russia for its actions”. But he also “underscored that there remains a clear path for resolving this crisis diplomatically”, according to the White House.

White House aides had reiterated earlier on Sunday that the US would not recognise the results of the referendum and promised to introduce sanctions against Moscow within days.

Dan Pfeiffer, a senior adviser to Obama, told NBC’s Meet the Press: “This referendum is in violation of international law.”

Amid pressure on Obama from Republicans to take tougher action against Putin, Pfeiffer declined to rule out American direct military aid to Kiev, saying only that the US was considering “all ways of assistance” in light of the Russian military occupation.



The Republican senator John McCain said on Saturday during a visit to Ukraine by a bipartisan group of eight senators that the country required a “long-term military assistance programme from the United States” comprising “lethal and nonlethal” equipment to enable resistance against Russian forces.



Pfeiffer said senior Russians should prepare for “sanctions designations in the coming days” from the US, which is poised to introduce asset freezes and visa bans authorised last week by Obama. And he urged Congress to pass an economic aid package for Ukraine, comprising $150m (£90m) along with $1bn in loan guarantees.



“We are putting as much pressure on the Russians as we can to do the right thing,” Pfeiffer said. Of Putin, he asked: “Is he going to continue to further isolate himself, further hurt his economy, further diminish Russian influence in the world, or is he going to do the right thing?”



Regarding diplomatic contact between the US and Russia, state media in Moscow said on Sunday that Sergei Lavrov, the Russian foreign minister, and John Kerry, the US secretary of state, had made progress during a telephone conversation about the crisis.



“Lavrov and Kerry agreed to continue contacts in search for a settlement of the situation in Ukraine through an earliest possible launch of constitutional reform, assisted by the world community in a generally acceptable form and with due respect for the interests of all regions of Ukraine,” the Russian foreign ministry said in a statement, according to Voice of Russia.



Ukraine’s prime minister, Arseniy Yatsenyuk, last week said his government was willing to “hold a national dialogue about additional rights and powers” that could be offered to Crimea.



However, on Sunday the Russian claims were met with scepticism in Washington. “We’ve seen this movie before: we should be cautious,” Mike Rogers, the chairman of the House intelligence committee, told CBS, suggesting that the Kremlin may simply be trying to buy time.



A senior State Department official told Reuters Kerry had told Lavrov the US would not accept the results of the referendum and “urged Russia to back constitutional reform in Ukraine that would protect the rights of minorities such as Crimea’s Russian-speaking population”.

Kerry also said Russia must pull back its forces to their bases and raised strong concerns about Russian military activities in Ukraine’s Kherson oblast on Saturday, as well as continuing provocations in eastern Ukraine, the official said.

McCain on Sunday again urged Obama to do more to punish Putin, reiterating his call for military aid and proposing the resumption of a US missile defence system in eastern Europe that was shelved when Obama came into office.



“The United States of America has to first of all have a fundamental reassessment of our relationship with Vladimir Putin. No more ‘reset’ button,” McCain told CNN’s State of the Union, referring to Obama’s efforts to begin a clean slate with Moscow at the outset of his first term.



Also back from the congressional visit to Ukraine, Senator Dick Durbin, the Democratic majority whip, dismissed Sunday’s referendum as “a Soviet-style election” in that “we know what the ending is going to be”.

He told Meet the Press that the Russian intervention in Crimea was “the single most serious act of aggression since the cold war”.