Defense Secretary Leon Panetta praised Brazil's emergence as a global power Wednesday, urging the nation to become more involved in security efforts around the world by assisting in places like Africa.

"We welcome Brazil's growing strength. We support Brazil as a global leader, and seek closer defense cooperation, because we believe that a stronger and more globally engaged Brazil will help enhance international security," Panetta said in a speech to Brazil's Superior War College. "With our deepening partnership, Brazil's strength is more than ever our strength."

In particular, he urged Brazil to work with the U.S. to help improve African militaries by conducting combined exercises and other training. U.S. officials have identified the terrorist threat coming out of Africa from al-Qaida linked groups as a growing international security problem.

Panetta said the U.S. and Brazil are at a critical point in their history and a stronger partnership could be a force for peace.

But even as he sketched out efforts to improve intelligence sharing and conduct combined military exercises and joint research, Panetta pushed back against Brazilian criticism of the U.S. and urged the country to buy American-made aircraft.

While his tone was largely friendly, it underscored the tensions that sometimes weigh on the relationship between the two democracies. And it comes as the U.S. frets about declining economic influence in South America, where China is steadily gaining as a top trading partner. China has surpassed the U.S. in trade with Brazil, Chile and Peru, and is a close second in Argentina and Colombia.

President Barack Obama has identified this region as increasingly important to U.S. national security. And Panetta continued that argument in his remarks Wednesday, as well as during meetings in Brasilia and Colombia earlier in the week.

Panetta said American and Brazilian officials must combine their technical expertise and increase information sharing about cybersecurity _ what he called the "battlefield of the future."

Panetta said both countries "have critical infrastructure that is targeted every day for intrusion and potential attack."

Still, Panetta's push for Brazil to make a decision on a long-delayed competition and choose to buy American-made F/A-18E/F Super Hornet fighter jets underscored a pressure point in the two countries' relations. The U.S. wants Brazil to buy 36 of the Boeing jets, with a contract valued at as much as $4 billion.

He argued that the U.S. willingness to partner with Brazil on the program would provide unprecedented advanced technologies. Brazil has complained that the U.S. must share more of its technologies.

"We fully understand that Brazil is not looking just to be the purchaser of a fighter aircraft, but rather a full-fledged partner in the development of cutting-edge aviation technology," said Panetta, adding that this program would show how important the Brazilian partnership is to the U.S. Continued...