U.S. braces for heightened threats in wake of Iran strikes

• How and when Iran will respond to the attack, which could provoke retaliation against U.S. troops in the region or prompt trade disruptions, remains unclear.

Driving the news: The Department of Homeland Security said in a Sunday advisory that the ongoing conflict is creating a "heightened threat environment" in the U.S.

• Low-level cyber attacks from pro-Iranian hacktivists against U.S. networks are likely, and attacks from state-affiliated actors could occur, the bulletin warned.
• DHS predicted the likelihood of violent extremists "in the Homeland independently mobilizing" would increase if Iran issued a "religious ruling" calling for retaliatory violence.
• Since the start of the conflict, the DHS memo read, several foreign terrorist organizations have called for violence against U.S. assets and personnel in the Middle East.

Zoom out: The State Department also issued a "Worldwide Caution" alert warning of the "potential for demonstrations against U.S. citizens and interests abroad."

• The U.S. Embassy in Qatar on Monday recommended American citizens there shelter in place until further notice "[o]ut of an abundance of caution." Following the U.S. security alert, the UK urged British nationals in Qatar to do the same.
• Several major cities, including the nation's capital, said they'd step up security in sensitive areas, including places of worship.
• Homeland Security and FBI officials discussed with some governors and law enforcement on Sunday how the strikes could escalate the threat environment, multiple outlets reported.
• DHS Assistant Secretary Tricia McLaughlin said in a statement to Axios that DHS Secretary Kristi Noem has spoken with governors and law enforcement nationwide "to ensure our partners at every level of government have the information they need to keep their communities safe."

Threat level: Iranian UN Ambassador Amir Saeid Iravani blasted the attacks at an emergency Security Council meeting, where he said that Iran's armed forces will determine the "timing, nature and scale" of its response.

• Iran's foreign minister Abbas Araghchi said at a news conference that Tehran "reserves all options to defend its security."
• President Trump, in a Saturday Truth Social post, warned that any retaliation against the U.S. will be met with "FORCE FAR GREATER THAN WHAT WAS WITNESSED TONIGHT."
• Secretary of State Marco Rubio said on CBS News' "Face the Nation" Sunday that there are no plans for the U.S. to engage in further attacks on Iran unless they attack Americans or U.S. military sites.

Go deeper: Trump administration says U.S. does not seek regime change in Iran

Editor's note: This story has been updated with a security alert from the U.S. Embassy in Qatar and a statement from DHS Assistant Secretary Tricia McLaughlin.