A police officer stands outside a property after the bomb squad were called to a search on Springfield Road in Wigan, Britain, May 30, 2017. REUTERS/Andrew Yates

(Reuters) - British police said Tuesday that they have released three men without charges that were taken into custody in connection with last week’s Manchester suicide bombing that killed 22 people.

Police have arrested at least 16 people in an investigation that continues more than seven days after the attack in a packed concert hall filled with children and young people.

“It will be a long investigation and it will take considerable time before we fully understand what has happened,” the Greater Manchester police said in a statement on Twitter.

Police have let go a total of five people without charges, including a man and woman released earlier.

Two men from Fallowfield area, aged 20 and 24, and a 37-year-old man from Blackley area were released Tuesday, the Greater Manchester police said.

(This version of the story was refiled to corrects the day in the first paragraph to Tuesday)