Opposition communications spokeswoman Melissa McIntosh has called on Australia Post to better explain what happened at its Bourke St Post Office in Melbourne after it quietly said it was “aware of unauthorised access and theft of some mail” this month.

The statement was uploaded to Australia Post’s website on Tuesday night, but the notice is not immediately apparent without clicking through several links.

“We have increased security and are working with Victoria Police to investigate,” Australia Post said. “We apologise for any inconvenience caused.”

It said the break-ins occurred between July 6 and July 17.

McIntosh said the lack of detail was “deeply concerning, given the trust people place in Australia Post in ensuring their mail reaches the correct destination safely and securely”.

Australia Post notified customers and upped security at the post office following the after-hours break-ins.

“An incident of unauthorised access and theft of mail from the GPO Box Room in one of our country’s major cities requires a swift and thorough response,” McIntosh said.