* Government worried about jihadists back from Syria, Iraq
* Authorities have been arresting returning fighters
* Last attack in Morocco was 2011 Marrakesh blast
By Aziz El Yaakoubi
RABAT, July 11 (Reuters) - Morocco has put its security services on high alert after intelligence reports revealed a "serious terror threat" from Islamist militants returning home after fighting in Iraq and Syria, the government said.
Hundreds of fighters from Morocco and other Maghreb states like Tunisia and Algeria have joined Islamist-dominated fighters in Syria's civil war and the insurgency in Iraq, and North African governments fear they will perpetrate attacks once they return.
"The threats are linked to the increasing numbers of Moroccans belonging to organisations in Syria and Iraq," said a statement issued after the weekly cabinet meeting. "Many of these fighters, including some who are leading those organisations, don't hide their willingness to perpetrate terrorist attacks against our country."
An al Qaeda offshoot now calling itself the Islamic State has proclaimed a "caliphate" on territory it has seized in Iraq and Syria after a lightning advance last month.
Moroccans fighting with the group have posted videos on social media showing their weapons and promising they will return to create an Islamic state in Morocco.
"We will bring this back to you in the kingdom of Mohammed VI," one militant with a northern Moroccan accent said in a video posted last week, referring to the Moroccan king.
Moroccan authorities say they have dismantled dozens of Islamist militant cells that sent fighters to Syria and Iraq.
"Authorities have arrested around 160 members who returned home," said Abderrahim Ghazali, spokesman for an association of families and former detainees that defends the rights of jailed Islamists. "Most of them have been arrested when their plane landed at Moroccan airports."
The North African kingdom has suffered numerous bomb attacks by suspected Islamist militants, most recently in 2011 in Marrakesh, when a blast in a cafe killed 15 people including 10 foreigners. It was the worst attack in Morocco since 2003, when suicide bombings killed more than 45 people in Casablanca. (Editing by Patrick Markey and Mark Trevelyan)