"The Special Groups are returning from Iran after receiving training in using new tactics. We have seized 20 motorcycle bombs in Nasiriyah. Some groups have arrived in Nasiriyah," Fatlawi said, referring to the capital of Dhi Qar, which neighbours Maysan.
The US military claims that Special Groups are cells of Shiite militants who are trained, funded and armed by Iranian-linked groups.
Tehran denies the charges.
"They are crossing the border through Amara," Fatlawi said.
"They intend to target officials in the country and in Nasiriyah," he said adding that local authorities had put in place tight security measures, including banning the use of motorcycles.
Shiite Special Groups have been one of the main perpetrators of violence in Iraq, but a series of military crackdowns in Shiite majority regions of Iraq forced many of the leaders of such groups to flee the country.
Iraqi and US officials claim many of them went to Iran.