Documents obtained by Reuters on Wednesday showed Prime Minister Mikhail Fradkov and several key ministries, including Lavrov's foreign ministry, doubted the scientific basis of the pact, which depends on Russian approval to come into force. The documents also said the pact was unlikely to bring Russian significant new investment or earnings.
But Lavrov repeated the position voiced by President Vladimir Putin in May, who told European Union leaders Moscow would accelerate the ratification process.
"(Saying Russia will not ratify) is not true, the announcement of President Vladimir Putin at his meeting with the EU troika in May remains in force," Lavrov told officials.
A government source on Thursday said it was split over Kyoto, with the influential Economy Ministry sticking to its support for the pact, although the Energy and Natural Resources Ministries had turned against it.
"The Economy Ministry sent a letter to the government explaining its position when they turned out to be so negative," said the source.
Under the terms of the pact, which aims to stabilize greenhouse gas levels in the atmosphere, it can only come into force if developed countries responsible for 55 percent of emissions ratify.
Since top polluter Washington pulled out in 2001, this has left Russia with the casting vote.