Russia and China are flexing their muscles with Washington as diplomatic relations between the world's greatest economic and political forces plunges to new depths as the US continues it hunt for elusive whistleblower Edward Snowden.
Lavrov said Snowden has not crossed the Russian border and insisted that Russia has nothing to do with him, his relations with US justice, or his travel plans.
He angrily criticised American demands for Snowden's extradition and warnings of negative consequences if Moscow fails to comply.
Mr Lavrov said that accusing Russia of "violation of US laws and even some sort of conspiracy" with regard to Snowden is "absolutely ungrounded and unacceptable".
He would not specify the location of Snowden, who booked a Havana-bound flight from Moscow yesterday but did not show up on the plane.
Mr Snowden was believed to be in Russia, where he fled on Sunday after weeks of hiding out in Hong Kong following his disclosure of the broad scope of two highly classified counter-terror surveillance programmes to two newspapers.
The programmes collect vast amounts of Americans' phone records and worldwide online data in the name of national security.
Mr Snowden had flown from Hong Kong to Russia, and was expected to fly early yesterday to Havana, from where he would continue on to Ecuador, where he has applied for asylum. But he did not get on that plane and his exact whereabouts were unclear.
The founder of WikiLeaks, the secret-spilling organisation that has embraced Mr Snowden, said the American was only passing through Russia on his way to an unnamed destination to avoid the reach of US authorities.
Despite its diplomatic tough talk, the US faces considerable difficulty in securing co-operation on Mr Snowden from nations with whom it has chilly relations.
The White House said Hong Kong's refusal to detain Mr Snowden had "unquestionably" hurt relations between the US and China.
While Hong Kong has a high degree of autonomy from the rest of China, experts said Beijing probably orchestrated Mr Snowden's exit in an effort to remove an irritant in Sino-US relations.
President Barack Obama and Chinese President Xi Jinping met earlier this month in California to smooth over rough patches in the countries' relationship, including allegations of hacking into each other's computer systems.
Secretary of State John Kerry urged Moscow to "do the right thing" amid high-level pressure on Russia to turn over Mr Snowden.
"We're following all the appropriate legal channels and working with various other countries to make sure that the rule of law is observed," Mr Obama told reporters when asked if he was confident that Russia would expel Mr Snowden.
His spokesman, Jay Carney, said the US was expecting the Russians "to look at the options available to them to expel Mr Snowden back to the US to face justice for the crimes with which he is charged".
He added: "The Chinese have emphasised the importance of building mutual trust. And we think that they have dealt that effort a serious setback.
"This was a deliberate choice by the government to release a fugitive despite a valid arrest warrant, and that decision unquestionably has a negative impact on the US-China relationship."
Mr Snowden has acknowledged revealing details of top-secret surveillance programmes that sweep up millions of phone and Internet records daily.
He is a former CIA employee who later was hired as a contractor through Booz Allen to be a computer systems analyst. In that job, he gained access to documents - many of which he has given to The Guardian and The Washington Post to expose what he contends are privacy violations by an authoritarian government.
Mr Assange and lawyers for WikiLeaks attacked the US for "bullying" foreign nations into refusing asylum to Mr Snowden. WikiLeaks counsel Michael Ratner said Mr Snowden is protected as a whistle-blower by the same international treaties that the US has in the past used to criticise policies in China and African nations.
Ecuador's president and foreign minister declared that national sovereignty and universal principles of human rights - not US prodding - would govern any decision they might make on granting asylum to Mr Snowden.
Ecuador has rejected some previous US efforts at co-operation and has been helping Mr Assange avoid prosecution by allowing him to stay at its embassy in London.
Formally, Mr Snowden's application for Ecuadoran asylum remains only under consideration. But Foreign Minister Ricardo Patino made little effort to disguise his government's position.
He told reporters in Hanoi that the choice Ecuador faced in hosting Mr Snowden was "betraying the citizens of the world or betraying certain powerful elites in a specific country".
Mr Patino said that he did not know Nr Snowden's exact whereabouts.
American experts said the US will have limited, if any, influence to persuade governments to turn over Mr Snowden if he heads to Cuba or nations in South America that are seen as hostile to Washington.