WASHINGTON-President Barack Obama took mounting American concern about computer directly to the Chairman of the China's hacking on Thursday in a sign of how seriously the United States takes the threat of cyber attacks originating from China.

A day after meeting with the American corporate CEO's in the White House Situation Room, Obama spoke by telephone about cyber threats with Chinese President Xi Jinping on the North Korea's nuclear challenge and cyber issue, currency and trade issues.

A White House statement said Obama "stressed the importance of addressing cyber security threats, which represent a shared challenge."

Earlier this week, U.s. intelligence leaders said for the first time that cyber-attacks and cyber espionage terrorism as the top security threat to the United States had supplanted.

American companies are becoming more concerned about the targeted theft of confidential business information and proprietary technologies by cyber dangers which emanate from China.

"The international community cannot afford to tolerate such activity of each country," White House national security adviser Tom Donilon said this week.

Obama called Xi to congratulate him on his new position and agreed on the value of regular consultations at a high level. To that end, Obama noted that U.s. Treasury Secretary Jack Lew will visit China next week to be followed in the next few weeks by the Secretary of State John Kerry, a White House statement said.

Lew is missing the international stature of its predecessor, Timothy Geithner, and the visit to China to boost its international visibility.

Obama welcomes the commitment of China to G-20 Nations to move toward a more flexible exchange rate, a development long sought by the United States to American export competitiveness in the Chinese markets.

Administration officials have said that China has made progress in the valuation of its currency, allowing the yuan to appreciate by about 15 percent against the dollar in recent years.

A big drop in global trade surplus of China and a rise in labor costs also helped with making Chinese products less competitive, even if the u.s. economy continues to improve, currency give less salience.

But Lew remains China's yuan undervalued, and has promised to push the country do more to appreciate its currency has said. U.s. lawmakers say that an artificially low yuan is hurting American manufacturers.

On top of that, the United States has come under fire from other countries for an aggressive relaxation of monetary policy critics argue would drive down the dollar, a charge that Washington put on a harder place to criticize in China.

Obama and Xi also talked about North Korea's nuclear challenge. After a new round of UN sanctions, North Korea was recently reported to have declared void the 1953 Armistice Agreement that ended the war with South Korea. — Reuters