"No one," Lavrov added, "including the United States, will challenge our right to continue building the atomic electricity station in Bushehr."
Lavrov was merely reiterating Russia's position on Iran's disputed nuclear program, which the West fears could be aimed at producing nuclear weapons.
But his tone struck many as unusually sharp, particularly against the backdrop of Rice's surprise visit to Moscow on 15 October.
Rice flew to Moscow to press Russian President Vladimir Putin to back Washington's attempts to haul Iran before the UN Security Council if it refuses to return to diplomatic talks over its nuclear program.
Putin, however, remained unswayed, saying the issue needed to be solved within the International Atomic Energy Agency (IAEA).
Yevgenii Volk, the director of Moscow's Hermitage Foundation, said Lavrov's televised statements indicated a firmer Russian position.
"No such tough comment [on Iran] has been made in the past," Volk said. "This is definitely a hardening of Russia's stance, a clear signal to the U.S. that there can be no agreement on this issue today and that Russia intends to continue its atomic cooperation with Iran. In my opinion, this is a very serious moment in [U.S.- Russia] bilateral relations."
Volk said Iran's nuclear program has become the main bone of contention between the United States and Russia, and predicted this issue will seriously sour both countries' relations in the future.
"The Russia-U.S. relations concerning the Iranian issue are not improving, they are, on the contrary, worsening," Volk said. "In the future, this will seriously complicate other problems that now exist in bilateral relations between Moscow and Washington."
Some other analysts agree that Moscow looks set to continue resisting any Western efforts to refer the Iran nuclear crisis to the UN Security Council.
Ruslan Pukhov, a defense analyst who heads the Center for Analysis of Strategies and Technologies in Moscow, said the protracted war in Iraq has weakened the United States in the eyes of Russia and emboldened Moscow to adopt a firmer tone on Iran.
"Maybe Russia can afford to express its dissatisfaction and its disagreement in a tougher manner because it understands in what difficult situation the U.S. now finds itself regarding the war in Iraq," Pukhov said.
Meanwhile, Russia today rejected a report published in the "Sunday Telegraph" on 16 October that former Russian military members helped Iran obtain ballistic-missile technology.
The report, which does not cite the sources of that information, claims Russia acted as a mediator between Iran and North Korea according to a deal they clinched in 2003.