San Francisco, Reuters—The FBI strengthened on Friday its warning to businesses that a hacking group loyal to the government of Syria might intensify its internet attacks as the United States weighs military strikes in that country.

In an email alert sent to its business contacts, the FBI said the Syrian Electronic Army has been “highly effective in compromising multiple high-profile media outlets,” referring to its hours-long hijacking of the main New York Times web page and an earlier takeover of an Associated Press Twitter account, among others.

It said the “the possibility of US military action in Syria may lead to further escalation of computer network operations by pro-Syrian or other aligned cyber actors.”

Reuters obtained a copy of the alert from a source who had received it from the FBI. An FBI spokeswoman confirmed the alert was legitimate but said it would not be posted publicly.

The alert was stronger in tone than one on the same group issued a week ago. It listed a number of websites that are under control of the SEA, allowing companies and service providers to block connections to them.

The FBI said that the Syrian group typically uses “spear-phishing” attacks, in which emails tailored to an individual or small group direct the recipients to a site that masquerades as a web-based email page and prompt the visitor for a logon and password. The hackers can then use those credentials to intercept or send emails and to try to login to Twitter and other services.

The FBI did not warn that the group was capable of crippling critical infrastructure, saying instead that its primary goal has been to spread propaganda.

Some former officials, however, have said that the group may be getting support from Syria’s key ally Iran, which has a much more advanced cyber-war program.