Iraqi authorities have made several arrests over recent attacks on US-linked outlets, including among security force personnel, the interior ministry said on Tuesday.
Dozens of men attacked two restaurants in Baghdad on Monday including a KFC, security officials said, as calls grow to boycott US brands over Israel's war in Gaza.
They were the latest in a spate of attacks targeting Western-linked brands in Iraq that started last week and have so far caused damage but no casualties.
The attacks intended to "harm American interests", the ministry said, adding that several suspects had been arrested over last week's attacks.
"Unfortunately, it appeared that some of them belong to one of the security apparatuses and had carried out these actions to harm American interests," the ministry said.
A security source said 13 suspects were arrested Monday, without providing details. Another security official said several people were detained but later released.
Monday's attack came shortly after the powerful pro-Iranian group Kataeb Hezbollah called on its supporters to "boycott and expel" what they denounced as "spy" entities affiliated with the "occupation".
The group, which Washington considers a "terrorist" organisation, has repeatedly called for US troops to leave Iraq.
Kataeb Hezbollah is part of the Islamic Resistance of Iraq, a loose alliance of pro-Iran groups that had claimed attacks on US troops over the Gaza war before suspending them in late January.
It is also part of the Hashed al-Shaabi, a coalition of paramilitaries now integrated into Iraq's regular security forces.
Since the war in Gaza started in October, a boycott movement spearheaded by pro-Palestinian activists has targeted major Western brands, such as Starbucks and McDonald's.
Iraq does not recognise the state of Israel, and all of its political parties support the Palestinian cause.