Russia has sent 300 military instructors to the Central African Republic at the request of the country's leadership to help counter a surge in rebel violence ahead of Sunday's election, Russia's foreign ministry said on Tuesday.
Officials and a security source in the Central African capital Bangui said earlier on Monday that Rwanda and Russia had dispatched troops and supplies.
The 300 Russian instructors coming at the request of Bangui authorities are to provide training to the national army.
They could bolster security forces and over 12,000 United Nations peacekeepers as armed rebel groups, some of whom fought one another in the country's prolonged conflict, have formed an alliance and are threatening to march on the capital.
"We are carefully following the unfolding situation in the Central African Republic," the Russian foreign ministry said in a statement. "We are seriously concerned that the events of recent days have led to a sharp deterioration in the security situation in this country."
The mineral-rich but deeply impoverished country has struggled to regain stability since 2013 when then-President Francois Bozize was ousted by a rebellion of mainly Muslim Seleka rebels.
Alleged human rights abuses by the Seleka sparked reprisals from the mostly Christian Anti-balaka militia, plunging the landlocked country into a spiral of tit-for-tat violence.
Clashes surged in the days after the country's highest court barred Bozize from running in Sunday's election.
President Faustin-Archange Touadera's government has accused Bozize of plotting a coup.
Some political parties have called for the election to be postponed due to the spate of violence, while the International Crisis Group think tank urged neighboring heads of state on Tuesday to help Bozize and Touadera strike a deal and calm the situation to ensure the election can proceed.
The United Nations mission in Central African Republic and the government insist that the vote will go ahead.
Security and diplomatic sources said on Tuesday a rebel group had seized control of Bambari, a trading hub around 380 kilometers (235 miles) east of the capital. The government could not be reached for comment.
Mankeur Ndiaye, the U.N. envoy in Central African Republic, told a news conference on Tuesday the security situation was relatively calm, and measures were in place to secure the vote.
"If the elections don't hold ... we risk entering a period of uncontrolled instability," Ndiaye said.
