The commitment will come as Prime Minister Theresa May meets French President Emmanuel Macron at an army base near the British capital, with immigration and global aid also on their agenda.
In a separate move, Italy’s parliament on Wednesday also approved a ramped up military presence in Niger by agreeing to send an initial 120 troops with 350 more to follow as Rome looks to stem migration and people-trafficking of African migrants.
European powers are desperate to stem the flow of African migrants crossing the Mediterranean and are spooked by increased militant jihadism across the Sahel region.
May is due to announce the deployment of three RAF Chinook helicopters to provide logistic support to French troops.
The mission is focused on Mali, where the UN, EU and African Union all have military operations countering terrorism and illegal trade in people, drugs, weapons and wildlife.
“Today’s summit will underline that we remain committed to defending our people and upholding our values as liberal democracies in the face of any threat, whether at home or abroad,” May said in a statement ahead of the summit.
May will also discuss with the French president their joint crackdown on online extremism “to ensure that the internet cannot be used as a safe space for terrorists and criminals,” according to the government spokesman.
Britain is also expected to allocate £50 million (56 million euros, $69 million) of additional aid for those affected by epidemics, natural disasters and conflict across west Africa.
Earlier this week five Sahel countries — Mali, Mauritania, Niger, Chad and Burkina Faso — launched their second anti-jihadist operation in the troubled region, after talks in Paris with their partner France.
The force has been operating, with heavy French backing, to re-establish control in lawless frontier regions in the Sahel, south of the Sahara, where terror groups have been able to flourish, particularly in the “tri border” area where Mali, Niger and Burkina Faso converge.
Italy’s focus is on Niger, a key transit country for tens of thousands of people arriving in Libya which is itself the launchpad for many Europe-bound African migrants, from where they attempt dangerous sea crossings to Europe.
Last year, some 115,000 landed in Italy, a figure down 32 percent year on year, taking arrivals since 2014 to around 600,000.
“This is a training mission in response to a request from Niger, not a combat mission,” said Defence Minister Roberta Pinotti, speaking about the plan lawmakers approved on Wednesday.
Italian troops, he added, would “reinforce instruments of territorial and border control and reinforce local police forces.”