Bamako (AFP) - The fight against jihadists in Africa's Sahel region is "achieving results", France's prime minister said in Mali on Saturday, two days after French forces killed a top extremist leader.

"The anti-terrorist struggle in the Sahel requires determination, endurance and humility. We are faced with a hard fight," Edouard Philippe told reporters.

The prime minister arrived late Friday in the capital Bamako along with Defence Minister Florence Parly, on a visit to show "support" for Mali, where some 2,700 French troops have been deployed since 2014 -- part of a 4,500-strong force spread across the region.

"Having an impact"

"We see that we are achieving results, that we are disrupting networks, I have no doubt that this presence has an impact", he said.

The French military "will remain as long as is necessary".

Philippe declined to comment in detail on the death in Mali Thursday of Djamel Okacha -- also known as Yahya Abou El Hamame -- an Algerian commander for Al-Qaeda in the Islamic Maghreb (AQIM).

Mali's government said Friday that French armed forces had killed Okacha in an air and ground ambush on a column of vehicles he was travelling in north of Timbuktu.

His death ended a years-long hunt for a man accused of masterminding the kidnapping of Westerners in the Sahel region.

Okacha, a jihadist veteran, was believed to be second in command of the Group to Support Islam and Muslims (GSIM), also known as Nusrat al-Islam.

The group was formed by the merger of Ansar Dine, the Macina Liberation Front, Al-Mourabitoun and El Hamame's Sahel branch of AQIM.

In addition to French troops in Mali, around 15,000 peacekeepers have been deployed in the country as part of the United Nations stabilisation mission known as MINUSMA.

This followed the signing of a peace accord in 2015 between the Bamako government and armed groups. 

But jihadist groups have continued operating in Mali and neighbouring countries.

Supported by France, Burkina Faso, Chad, Mali, Mauritania and Niger have formed the so-called G5 Sahel group to fight the jihadists.

Philippe also unveiled 85 million euros ($96 million) of French aid including 50 million in loans and 35 million in grants via the French Development Agency at a meeting with his Malian counterpart Soumeylou Boubeye Maiga and President Ibrahim Boubakar Keita.

The agency would double its contributions to Mali "in the coming years", he added.

He stressed that "it is important to win the war -- but also important to construct peace and prosperity."

The extent of the task ahead was underlined, however, by news that gunmen had killed three off-duty UN blue helmet troops and injured another as well as their driver Friday night on the road from Bamako to the Guinean border.

UN and security sources said the attack appeared to be a criminal assault.

The victims belonged to the 900-strong Guinean contingent within MINUSMA.

A MINUSMA statement said the trio were attacked around 10:00 pm by "unidentified armed men" near Siby some 44 kilometres (27 miles) south west of Bamako.

There have been more than 190 deaths since the mission began in 2013, more than half the overall UN deaths in similar missions worldwide in the same timeframe.

Philippe was due later Saturday to visit the French base at Gao, in the north, and dine with troops there, a visit initially scheduled for Sunday, his office said.