Accusing Moscow of funding the mercenaries, western countries including Canada, Germany, France and the UK said the deployment of fighters can only further deteriorate the security situation in West Africa.
Over a dozen Western powers have strongly condemned the deployment in Mali of Russian mercenaries working for the controversial company Wagner, accusing Moscow of providing material backing for the fighters.
The powers, who included Canada, Germany, France and the UK, said on Thursday that they "firmly condemn the deployment of mercenary troops on Malian territory".
It was one of the first official acknowledgements by Western capitals that the deployment of fighters is ongoing in Mali after months of warnings to the Bamako government.
"This deployment can only further deteriorate the security situation in West Africa, lead to an aggravation of the human rights situation in Mali (and) threaten the agreement for peace and reconciliation in Mali," the 15 powers said.
Their statement said the powers "deeply regret" the choice of the Malian authorities to use "already scarce public funds" to pay foreign mercenaries instead of supporting the Malian armed forces.
In a stern message to Moscow, the statement added: "We are aware of the involvement of the Russian Federation government in providing material support to the deployment of the Wagner group in Mali and call on Russia to revert to a responsible and constructive behaviour in the region."
Thursday's statement was issued by France, Belgium, the UK, Canada, Czech Republic, Denmark, Estonia, Germany, Italy, Lithuania, Netherlands, Norway, Portugal, Romania and Sweden.
Washington was not a signatory of the statement but US Secretary of State Antony Blinken earlier this month warned Mali not to accept Wagner mercenaries, saying a deal would divert needed funds and further destabilise the country.
The Wagner Group has caused controversy through its involvement in Syria, Libya, the Central African Republic as well as the conflict in eastern Ukraine.
EU ministers in November agreed on Monday to draw up more sanctions against Wagner.
Russia denies any government link with the Wagner Group but the unit has been linked to Yevgeny Prigozhin, a businessman close to President Vladimir Putin who has been hit by separate sanctions over meddling in the 2016 US election.
Prigozhin, who has been dubbed "Putin's chef" due to Kremlin catering contracts, denies any association with Wagner.
Mali is the epicentre of a militant revolt that began in the north of the country in 2012 and spread three years later to neighbouring Niger and Burkina Faso.
France intervened in 2013 by deploying troops whose numbers are now being reduced.