"The combination of those activities by those two countries, I think that bears watching. And certainly, I think their influence can be destabilizing," Austin told a panel with several presidents at the start of a three-day US-Africa summit.

Austin said that China was raising its footprint in Africa "on a daily basis" through its growing economic influence.

"The troubling piece there is they're not always transparent in terms of what they're doing and that creates problems that will be eventually destabilizing if they're not already," Austin said.

Austin said that Russia is "continuing to peddle cheap weapons" and deploying "mercenaries across the continent."

"And that is destabilizing as well," Austin said.