WASHINGTON (Reuters) - The United States Air Force has ordered its aircraft to stand down for one day within the next few weeks for a safety review after a string of deadly aircraft crashes.

Some aircraft might be exempted from the one-day pause in flights, such as those carrying out strikes in Iraq and Syria, said Major General John Rauch, the Air Force’s chief of safety, on Tuesday.

The operational pause must carried out by May 21 and comes after a Puerto Rico Air National Guard cargo plane crashed near Savannah, Georgia last week, scattering fiery debris over a highway and railroad tracks, and killing all nine people aboard.

The crash was at least the fifth deadly accident involving a U.S. military aircraft since early April.

According to Air Force data, there has been a 48 percent increase in the rate of aircraft crashes in fiscal year 2018 where someone was killed, permanently disabled or that caused over $2 million in damages.

U.S. military officials have said the crashes across the different branches of the military are not a crisis.

“This is not a crisis. But it is a crisis for each of these families... these are across services, and these are different individuals and different circumstances,” Pentagon spokeswoman Dana White said last week.