PARIS - French forces destroyed a convoy in Niger transporting weapons from Libya to Mali and captured fighters linked to al Qaeda, the presidency said on Friday as France steps up efforts to stop militants crisscrossing the Sahel-Sahara region. Paris, which has led efforts to push back Islamist fighters in the region since intervening in its former colony Mali last year, started redeploying troops across West Africa in July to form a counter-terrorism force, leaving UN peacekeepers to deploy across Mali’s north to secure the country. There has been a marked increase in attacks in recent months in the north.