The grandfather of seven children of a Swedish-Norwegian couple that had joined the Islamic State group and were killed in Syria says they have returned to Sweden.

The grandfather, Patricio Galvez, says the children, aged between 1 and 8, will be taken care of by social services and now needed "peace and quiet."

Galvez spoke to Swedish broadcaster SVT upon arriving on Wednesday in Goteborg, Sweden's second largest city on the west coast.

Last month, Galvez was allowed to travel to Iraq to pick up the children of his daughter Amanda Gonzales, a Swede, and her Norwegian husband Michael Skramo. The two were reported killed earlier this year.

The children were living at a refugee camp in northern Syria before being transferred to the city of Irbil in Iraq.