The Pentagon has quietly empowered the United States Cyber Command to take a far more aggressive approach to defending the nation against cyberattacks, a shift in strategy that could increase the risk of conflict with the foreign states that sponsor malicious hacking groups.

More than 30 high-tech companies, led by Microsoft and Facebook, announced a set of principles on Tuesday that included a declaration that they would not help any government — including that of the United States — mount cyberattacks against “innocent civilians and enterprises from anywhere,” reflecting Silicon Valley’s effort to separate itself from government cyberwarfare.

Although cyber weapons can usually be employed in a far less lethal manner than guided missiles shot from a drone, they have been deployed less frequently and under rules of engagement that are far less clear, at least to the public.

What started out as a counterintelligence investigation to guard the United States against a hostile foreign power has morphed into a political scandal about what Mr. Trump did, what he said and what he meant by it. 

Iran’s top nuclear negotiator was heading back to Tehran on Sunday to consult with his nation’s leadership, as negotiators remained divided over how to limit and monitor Tehran’s nuclear program and even on how to interpret the preliminary agreement they reached two months ago.

Five former members of President Obama’s inner circle of Iran advisers have written an open letter expressing concern that a pending accord to stem Iran’s nuclear program “may fall short of meeting the administration’s own standard of a ‘good’ agreement” and laying out a series of minimum requirements that Iran must agree to in coming days for them to support a final deal.

American officials have long considered Huawei, the Chinese telecommunications giant, a security threat, blocking it from business deals in the United States for fear that the company would create “back doors” in its equipment that could allow the Chinese military or Beijing-backed hackers to steal corporate and government secrets.