China and Russia rejected US accusations they helped a former U.S. spy agency contractor escape prosecution in the United States, deepening a rift between powers whose cooperation may be essential in settling global conflicts including the Syrian war.
Despite public outrage, however, there was a sense moscow and Washington sought to limit damage over Edward Snowden, whose flight from justice has embarassed President Barack Obama.
After tough US statements a day earlier, Secretary of State John Kerry urged "calm and reasonableness" on Tuesday. Snowden, charged with disclosing secret US surveillance programmes, left Hong Kong for Moscow's Sheremetyevo airport on Sunday.
The U.S. State Department said diplomats and Justice Department officials were talking to Russia, suggesting they sought a deal to secure his return to face espionage charges.
An airport source said the 30-year-old American, who has asked for asylum in Ecuador, had flown in on Sunday and had been booked on a flight to Cuba on Monday but had not got on board. Journalists camped out at the airport have not spotted him inside, or leaving, the transit area, and say a heavy security presence has been relaxed for the past 24 hours.
He has not registered at a hotel in the transit zone, hotel sources say. A receptionist at the Capsule Hotel "Air Express", a complex of 47 basic rooms furnished predominantly with grey carpets and grey walls, said Snowden had turned up on Sunday, looked at the price list and then left.
US officials admonished Beijing and Moscow on Monday for allowing Snowden to escape their clutches but the United States' partners on the UN Security Council, already at odds with Washington over the conflict in Syria, hit back indignantly.
"The United States' criticism of China's central government is baseless. China absolutely cannot accept it," Foreign Ministry spokeswoman Hua Chunying said in Beijing, also dismissing U.S. criticism of Hong Kong, a Chinese territory, for letting Snowden leave.
In the first comment on the affair by a senior Russian officials since Snowden arrived, Foreign Minister Sergei Lavrov denied suggestions Moscow had helped Snowden in any way, including by allowing him to fly into Sheremetyevo.
"He chose his itinerary on his own. We learnt about it ... from the media. He has not crossed the Russian border," he said. "We consider the attempts to accuse the Russian side of violating US laws, and practically of involvement in a plot, to be absolutely groundless and unacceptable."
There is growing speculation in the Russian media that Snowden may be talking to the FSB security service, a successor of the Soviet-era KGB, and could be involved in a prisoner swap.
"Lavrov always chooses his words carefully," said a Russian security source. "From his statement you can deduce the following: that he (Snowden) is either outside Russia or still in the transit zone. He is a tasty morsel for any, any secret service, also for ours."
Deputy parliamentary speaker Vladimir Zhirinovsky has proposed Snowden be exchanged for Viktor Bout, a Russian jailed in the United States for drug trafficking, requests for whose extradition have been ignored.
Fallout from a protracted wrangle over Snowden could be far-reaching, as Russia, the United States and China hold veto powers at the UN Security Council and their broad agreement could be vital to any settlement in Syria.
International mediator Lakhdar Brahimi said on Tuesday he was pessimistic an international conference on Syria could take place in July as hoped and urged Russia and the United States to help contain a conflict which has killed almost 100,000 people. Kerry said there was no cause to raise tensions over "something that is frankly basic and normal as this."
"It is accurate there is not an extradition treaty between Russia and the United states, but there are standards of behaviour between sovereign nations," he said, in Jeddah.
Lavrov's insistence Snowden had not entered Russia implies he has not left the airport transit area, used by passengers flying from one non-Russian airport to another without going through passport control or requiring an entry visa.
The transit area is Russian sovereign territory, but it could be argued that in staying there Snowden had not formally entered the country - a move that could implicate President Vladimir Putin in helping a fugitive. Russia appears, at least for the moment, reluctant to take such a step.
Interfax news agency quoted a source "in the Russian capital" as saying Snowden could be detained to check the validity of his passport if he crossed the Russian border.
Snowden is travelling on a refugee document of passage provided by Ecuador, the anti-secrecy group WikiLeaks said. Snowden, whose exposure of the surveillance raised questions about civil liberties in the United States, flew to Moscow after being allowed to leave Hong Kong even though Washington had asked the Chinese territory to detain him.
Snowden, until recently a contractor with the US National Security Agency, had been expected to fly to Havana from Moscow on Monday and eventually go on to Ecuador, according to sources at the Russian airline Aeroflot.
There is no direct flight from Moscow to Quito, which has said it was considering Snowden's asylum request. The Quito government has been sheltering WikiLeaks founder Julian Assange at its London embassy for the past year.
US officials said intelligence agencies were concerned they did not know how much sensitive material Snowden had and that he may have taken more documents than initially estimated which could get into the hands of foreign intelligence.