Takata has published an open letter from its chief executive officer in US and German newspapers.

According to Bloomberg News, Shigehisa Takada, chairman and grandson of the company founder, wrote the supplier is tripling capacity to test its airbag inflators. The devices have ruptured in five fatal accidents and have led to recalls of more than 20million vehicles.

"Even one failure is unacceptable and we are truly and deeply saddened that five fatalities have been attributed to auto accidents where Takata air bags malfunctioned,"  Takada wrote. "We understand the public’s concerns and we take them seriously."

The advertisements in newspapers including the New York Times, the Wall Street Journal and Detroit Free Press show Takata is intensifying efforts to defend itself amid a crisis that’s sent its shares plunging 56% this year, Bloomberg said. Takata hired public relations firm Sard Verbinnen & Co this month and said Alby Berman, vice president of global communications, is retiring while still consulting for the Tokyo-based company.

The open letter followed Takada’s interview this week with Japan’s Nikkei business newspaper, in which he said Takata had been misunderstood and had no intention of confronting the US National Highway Traffic Safety Administration (NHTSA). The company has refused NHTSA’s demands to expand some recalls nationwide that have been limited to high-humidity regions. The regulator said this week it was preparing for a legal battle.

Takata has said it will increase replacement airbag production to 450,000 repair kits by next month from its plant in Mexico. The company also will boost capacity to build the components at factories in China and Germany within a year, Takada told the Nikkei.

Honda, Takata’s biggest customer, has also has said it would source some replacement parts from Autoliv and Daicel.