WASHINGTON -- Obama administration officials acknowledged Tuesday that China’s involvement in cyber-attacks on sensitive U.S. companies is a near-constant subject of conversation between the nations’ officials but that there have been few signs that China is willing to stop the attacks.

“We have repeatedly raised our concerns at the highest levels about cyber-theft with senior Chinese officials, including in the military, and we will continue to do so,” White House spokesman Jay Carney said.

Carney’s statement came on the day that an Alexandria, Va., Internet security firm released one of the most detailed reports to date asserting that hacking is officially condoned in China. In the report, Mandiant Corp. said it had tracked online attacks on at least 141 companies and organizations since 2006 to a People’s Liberation Army organization known as Unit 61398. Of those 141 targets, 115 were in the United States, according to Mandiant’s 74-page report.

“Our research and observations indicate that the Communist Party of China . . . is tasking the Chinese People’s Liberation Army . . . to commit systematic cyber espionage and data theft against organizations around the world,” the report said.

The accusations will further strain tensions between the United States and China, a nation of growing economic and military influence.

“China is a rising power. It’s using everything at its disposal to be competitive,” said Harold Brown, a former defense secretary who led a U.S. commission to investigate China’s cyber, military and economic capabilities. “It’s weak in some ways, so it looks to gain advantages in other ways.”

In a regularly scheduled news briefing Tuesday, the Chinese government denied official involvement in online hacking and pointed out that China itself is regularly subjected to such attacks.

“Groundless criticism is irresponsible and unprofessional, and it will not help to solve the problem,” Foreign Ministry Spokesman Hong Lei said.

White House officials declined to comment on specific allegations in the report but called cyber security a “major challenge.”

“The United States has substantial and growing concerns about the threats to U.S. economic and national security posed by cyber-intrusions, including the theft of commercial information,” Carney said. “That’s why the United States government is taking an active approach in addressing the issue of cyber-theft.”

State Department spokeswoman Victoria Nuland said hacking came up at virtually every meeting of Chinese and U.S. officials.

“What we have been involved with is making clear that we consider this kind of activity a threat, not only to our national security but also to our economic interests,” Nuland said.

Administration officials say they’ve strengthened government networks, released technical information to private companies and engaged every agency and department in fighting cyber threats through diplomatic, military and economic means.

Last week, President Barack Obama signed an executive order aimed at improving the security of the computer networks that direct the nation’s crucial infrastructure systems, such as electricity, finance and transportation. The order, which doesn’t need congressional approval, directed federal agencies to share more information and companies to voluntarily comply with a government-led framework to combat online threats.