OUAGADOUGOU, Burkina Faso — Russia has been steadily expanding its military influence across Africa, alarming Western officials with increasing arms sales, security agreements and training programs for unstable countries or autocratic leaders.

In the Central African Republic, where a Russian has been installed as the president’s national security adviser, the government is selling mining rights for gold and diamonds at a fraction of their worth to hire trainers and buy arms from Moscow. Russia is seeking to ensconce itself on NATO’s southern flank by helping a former general in Libya fight for control over his government and vast oil market.

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Sudan’s president, Omar Hassan al-Bashir, brought in Russian mercenaries in January to help shore up his rule against nationwide protests. And last spring, five sub-Saharan African countries — Mali, Niger, Chad, Burkina Faso and Mauritania — appealed to Moscow to help their overtaxed militaries and security services combat the Islamic State and Al Qaeda.

Russia, entrenched in Africa during the Cold War’s violent East-West rivalry, largely retreated from the continent after the collapse of the Soviet Union. But in the past two years, Moscow has rekindled relations with Soviet-era clients like Mozambique and Angola, and forged new ties with other countries. President Vladimir V. Putin of Russia will host a summit meeting between Moscow and African countries later this year.