President Obama wrote a letter this week to formally apologize for the burning of Qurans at a U.S. military base in Afghanistan.

In the letter, written to Afghan President Hamid Karzai, Obama said he wanted to “express my deep regret for the reported incident.”

“I extend to you and the Afghan people my sincere apologies. The error was inadvertent; I assure you that we will take the appropriate steps to avoid any recurrence, to include holding accountable those responsible,” Obama wrote in the letter, according to a statement released by the Afghan president’s office.