By Julien Ponthus and Tiemoko Diallo
PARIS/BAMAKO (Reuters) - French President Francois Hollande said on Wednesday a military campaign against Islamist rebels in Mali has killed "terrorist leaders", without clarifying whether he was referring to two al Qaeda commanders reported dead last week.
He added the roughly 4,000 French troops in the West African state as part of the eight-week-old operation would begin withdrawing in April - a month later than planned - as a U.N.-backed African coalition force replaces them.
"We have launched an offensive in two directions, the first in the Ifoghas mountain range, and there we have had successes that will be further confirmed in the coming days, including the killing of terrorist leaders," Hollande told a news conference in Warsaw where he was attending a regional leaders event.
Chad has said its soldiers, fighting alongside the French, have killed two top commanders from al Qaeda's north African wing, Abdelhamid Abou Zeid and Mokhtar Belmokhtar, but Paris has so far said it could not confirm the reports.
The war against Islamist rebels in northern Mali claimed the life of a fourth French soldier on Wednesday.
The sergeant from the 68th African artillery regiment was a liaison agent for around 200 Malian soldiers operating about 100 kilometers (62 miles) from the eastern town of Gao, and died after being injured and taken away for treatment.
Around 30 Islamists were also killed in the fighting after Malian soldiers backed by French Mirage jets and helicopters retaliated, French army spokesman Colonel Thierry Burkhard told reporters.
Scores of Islamist fighters linked to al Qaeda's North African affiliate, Al Qaeda in the Islamic Maghreb (AQIM), have so far been killed as French and African forces fight to drive them out of northern Mali's rugged deserts and mountain ranges, a region they seized last April.
AQIM has pledged to avenge the French assault, which Paris says it launched to prevent its former colony becoming a base for wider Islamist attacks.
A U.N.-backed African force, AFISMA, has about 6,000 troops on the ground mainly securing recaptured towns in central Mali, though Chadian troops have advanced alongside the French into Mali's mountainous border region with Algeria.
Russia, which holds the rotating presidency of the U.N. Security Council this month, said on Wednesday it was ready to discuss a U.N. peacekeeping force for Mali after France said a month ago it hoped AFISMA would be replaced by a U.N. mandate by April.
"We are ready for discussion in the U.N. Security Council of the issue of putting the peacekeeping mission in Mali under the aegis of the United Nations," Russian Foreign Ministry spokesman Alexander Lukashevich told journalists at a weekly briefing.
Lukashevich suggested a decision could come near the end of March, when Russia holds a Security Council discussion on Mali that would include discussion of "giving the operation in that country a U.N. component".
He did not say exactly how the proposed peacekeeping force might relate to AFISMA.
With early signs of a guerilla-style rebel fight back, some experts have questioned whether a U.N. peacekeeping mission could be put in place before combat operations are concluded.
A permanent Security Council member with veto power, Russia has blocked resolutions on the Syrian conflict and opposed military intervention there, but in December backed a French-drafted resolution that authorized the African-led Mali force.
The fighting in Mali has raised fears for the welfare of foreign hostages held by al Qaeda-linked groups in Africa, including seven French believed to be in Mali.
(Reporting by Jean-Baptiste Vey, Julien Ponthus, and Tiemoko Diallo; Writing by Catherine Bremer and Richard Valdmanis; Editing by Sophie Hares)