Some messages sent by people working in the Welsh government during the pandemic may have been deleted, the first minister has said.
Mark Drakeford said he himself did not use WhatsApp, and would not know how to automatically delete texts.
But he could not promise that messages were not lost before the government was aware of what the Covid inquiry wanted.
Opposition parties said the comments were deeply concerning and alarming.
The comments follow a row in Scotland over the deletion of messages.
WhatsApp messages between UK officials and ministers have been a key part of recent evidence heard by the Covid inquiry.
The Scottish government has been criticised for not handing over all relevant data and former first minister Nicola Sturgeon has refused to say whether or not she had erased any messages.
A submodule of the Covid inquiry looking at the response in Wales is expected to begin public hearings in February 2024.
In the Senedd's First Ministers Questions on Tuesday Mr Drakeford said the Welsh government had made an "early decision" to "disclose all material requested by the UK Covid inquiry including WhatsApp messages".
Welsh Conservative Senedd leader Andrew RT Davies asked if Mr Drakeford was "confident that deletion mechanisms or apps were not used by government ministers... or officials".
Mr Drakeford said the Welsh government did not rely on "informal means of communication in order to make decisions during the Covid period".
He said that as soon as his government was aware that the inquiry would wish to have material disclosed to it "no instruction of any sort was issued in the Welsh government that material should be deleted".
"So as soon as we knew that the inquiry wanted something, there's no deletion beyond that point."
Former UK Prime Minister Boris Johnson announced the inquiry in May 2021, and it formally commenced in June 2022.
Mr Drakeford added: "During the Covid period itself, many colleagues working for the Welsh government would have had devices with deletion instructions already on them.
"And those things may have remained on their phones, because at that point absolutely nobody was focused on whether those messages might be required at some future distant point".
The first minister's official spokesman later added that "staff were regularly reminded of the need to maintain and retain robust records relating to decisions taken throughout the pandemic".
Pressed further by Mr Davies, Mr Drakeford added: "I think the fair way of putting it is, deletion may have taken place.
"I've never had any deletion arrangements on the phone because I would have no idea how to make it happen itself. I don't use WhatsApp, either."
After First Minister's Questions, Mr Davies wrote to the first minister challenging his assertion that he does not use WhatsApp.
The Conservative MS asked Mr Drakeford to correct the record after he said he was "provided with a screenshot which demonstrates that you have a WhatsApp account".
"Your statement that you do not use WhatsApp therefore gave the wrong impression," Mr Davies said.
A Welsh government spokesperson said the first minister would respond to the letter "in due course".
'Learn the lessons'
Plaid Cymru health spokesman, Mabon ap Gwynfor, said: "It is deeply alarming that some WhatsApp messages exchanged among Welsh government officials during the pandemic may have been lost.
"This is why we need a comprehensive Welsh public inquiry into our government's handling of the Covid-19 pandemic."
In an earlier statement, Mr Davies said: "To learn the lessons of the pandemic, all messages sent and received by ministers, special advisers and civil servants should have been retained.
"It's deeply concerning the first minister was unable to provide assurances that this is the case."