With a new constitution, I will no longer work with you as president.
Belarus has been rocked by months of anti-government protests after veteran leader Lukashenko claimed victory in an August 9 presidential election that his opponents say was rigged, a charge he denies.
According to Lukashenko, changes to the Belarusian constitution must be "beneficial for the country", to keep it from collapsing "later on".
"I do not make any Constitution for myself".
Mr Lukashenko has repeatedly raised the prospect of a new constitution since he won a sixth term in the presidential election on August 9.
Sergei Lavrov held talks with Lukashenko and other top officials in the capital Minsk, in the latest show of Russia's support for authorities in its ex-Soviet neighbour.
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It remained unclear whether Lukashenko's comments were honest or whether he was just paying lip service to the prospect of him stepping aside.
The longtime leader of Belarus is hinting at plans to step down after months of protests against his rule.
More than three months after an historic protest movement emerged across Belarus, people continue to take to the streets. Protests against the president are taking place in several cities, including the Razdhani Minsk, nearly daily. He has promised to reform the constitution to reduce the full powers of the president, but has insisted that his strong hand is needed to see the process through.
Lukashenko did not specify a timetable for reforming the constitution or leaving office, although he ventured there would be "trouble" if he left office too quickly. During a visit to Minsk on Thursday, Lavrov urged Lukashenko to move ahead with "constitutional reforms and modernizing the political system", a comment Deutsche Welle interpreted as "a signal to Lukashenko that Moscow's patience is wearing thin".
Lukashenko's regime denies torturing prisoners and claims protesters are backed by foreign powers.
Lavrov said the West is "using dirty methods of so-called colour revolutions, including manipulating public opinion, supporting forces that are openly anti-government and promoting their radicalisation".