DETROIT » At the insistence of U.S. safety regulators, Honda is adding more than a million of its most popular vehicles to a growing recall for air bags that can explode with too much force.

The company said Monday it’s expanding a previous recall of passenger air bag inflators from high-humidity states to the entire nation. That will add just over a million 2001 to 2005 Civics and 2003 to 2007 Accords to the recall. The two sedans are Honda’s No. 2 and No. 3 sellers so far this year in the U.S.

Two weeks ago Honda said it would recall about 350,000 of the cars in high humidity areas. But the recall was expanded after the National Highway Traffic Safety Administration demanded that it be done nationally. A driver’s side recall already is being done across the nation.

The ammonium nitrate propellant in air bag inflators made by Takata Corp. can burn too quickly, blowing apart a metal canister and sending shrapnel into drivers and passengers. The problem has been blamed for at least seven deaths and more than 100 injuries worldwide.

In May, Takata bowed to government pressure and declared many of its products defective, agreeing to double the number of air bag inflators being recalled to 33.8 million, making it the largest auto recall in U.S. history. Some cars are equipped with both driver and passenger air bags made by Takata.

Last week Honda confirmed that a Louisiana woman was the seventh person killed by a defective Takata inflator. Kylan Langlinais, 22, of Lafayette, Louisiana, died at a hospital on April 9, four days after the 2005 Accord she was driving crashed into a utility pole in the city, according to a lawsuit filed by her family.

The giant recall covers driver and passenger air bags in cars and trucks made by 11 automakers. Takata, the automakers and NHTSA are still trying to determine what exactly causes the inflators to malfunction.

So far Honda has recalled about 21 million vehicles across the globe because of the potentially defective inflators. The company is Takata’s biggest customer.