The mayor of Cleveland apologized Thursday to the family of Tamir Rice, a black 12-year-old boy fatally shot by a white Cleveland police officer, for the city having sent the administrator of the boy's estate a "decedent's last dying expense" claim of $500 for ambulance services.

Mayor Frank Jackson opened a City Hall news conference by saying, "We want to start off again apologizing to the Rice family if in fact this has added to any grief or pain they may have."

Jackson said the claim was a "routine" matter but that supervisors should have been alerted to whom it involved and that it shouldn't have been filed. He said the claim would be withdrawn.

"It was a mistake in terms of us flagging it, but not a mistake in terms of the legal process," Jackson said.

Tamir was shot outside a city recreation center by a then-rookie patrolman, Timothy Loehmann, in November 2014 while playing with a pellet gun. Loehmann and his training officer, Frank Garmback responded to a 911 call about a man waving a gun and pointing it at people. A grand jury in late December declined to indict Loehmann and Garmback on criminal charges.

The administrator for Tamir's estate, Douglas Winston, told The Associated Press on Thursday that he asked Cleveland for documents related to Tamir's medical care and had never previously seen such a request result in a claim being filed in Probate Court, which is what occurred on Wednesday.

"I just wanted to know what the bill was and who might have paid it," Winston said.

Winston added that he would have rejected the claim because it was filed too late. Ohio law says such claims must be filed within six months of a person dying.

Cleveland's finance director said at the news conference that the file for the ambulance bill was closed in February 2015 after Medicaid paid $179 of the $500 cost. The city wrote off the balance, she said.

Rice family attorney Subodh Chandra, who also represents the estate, said filing the claim made no sense to the family. Both the family and the estate have sued the city and the police officers in federal court over Tamir's death.

"This was a deeply disturbing incident to them," Chandra said.

It's not the first time that Jackson has held a news conference to apologize to the Rice family. He apologized in March 2015 after city attorneys filed a response to the lawsuit that blamed Tamir for his own death. Jackson called the response "insensitive" at the time and ordered it refiled.