Iraqi security forces arrested several suspects in connection with a double suicide bombing in the capital Baghdad last week that shattered a period of relative calm.
Among those is the man accused of driving the attackers to the scene from Baghdad’s southern suburb of Yusufiya, said Badr Al Zayadi, an MP who sits on Parliament’s Security and Defence Committee.
Mr Al Zayadi said that authorities believe the group had been planning the attack since August and had intended to carry it out on January 1.
They also planned another suicide attack in Baghdad's western Karkh area, he said, but did not explain why the second attack did not take place.
Iraqi security forces recently arrested 60 ISIS militants, including senior leaders, who came from Turkey, and foiled about 600 attacks, he said.
He gave no further details, saying investigations were still under way.
Thursday's attack was the first since January 2018, a month after Iraqis declared full victory over ISIS, driving it from major cities and towns.
The ISIS-claimed attack last week killed 32 civilians and injured more than 100.
The attackers blew themselves up minutes apart in a crowded outdoor market in central Baghdad frequented by mainly poor people seeking second-hand clothing and goods.
The first bomber pretended to be ill, gathering a crowd around him of people trying to help before setting off his explosives. When people rushed to help the wounded, the second man blew himself up.
Under pressure from the public, Iraqi President Barham Salih on Saturday ratified 340 death sentences for people convicted of terrorism and criminal charges. On Monday, three Iraqis convicted of terrorism were hanged.
The Baghdad attacks came during a sensitive time as Iraqis prepare for national elections in October amid a planned withdrawal of US troops from the country.