Ash Carter, who served as defence secretary under the Obama administration, opening military combat jobs to women and ending a ban on transgender people serving, has died aged 68.

Mr Carter died after suffering a heart attack on Monday evening, according a statement from Douglas Elmendorf, dean of Harvard University’s Kennedy School. Carter had served as as director of the school’s Belfer Center for Science and International Affairs.

In December 2015 Mr Carter ordered the military to open all jobs to women, removing the final barriers that kept women from serving in combat, including the most dangerous and gruelling commando posts.

“I made the decision to admit women to all military specialties without exception,” Mr Carter said in an interview on the decision. “They are 50% of the population. We can’t afford to leave off the table half of the population who can, if they’re the ones who have the best qualifications, do the job.”

The following year, Mr Carter was responsible for ending the ban on transgender troops serving in the US military, saying it was the right thing to do.

“Americans who want to serve and can meet our standards should be afforded the opportunity to compete to do so,” Mr Carter said in June 2016, laying out a one-year plan to implement the change.

“Our mission is to defend this country, and we don’t want barriers unrelated to a person’s qualification to serve preventing us from recruiting or retaining the soldier, sailor, airman or Marine who can best accomplish the mission.”

Mr Carter also often spoke with pride on his role in speeding the acquisition of armoured vehicles for Iraq and Afghanistan during the height of both conflicts to better protect US troops from roadside bombs.

Mr Carter served as the 25th defence secretary and “loved nothing more than spending time with the troops, making frequent trips to Iraq and Afghanistan to visit US forces with his wife Stephanie,” his family said in a statement.

“Ash Carter always set politics aside; he served presidents of both parties over five administrations.”

President Joe Biden said Mr Carter took seriously his “sacred obligation” to the men and women in uniform.

“He was relentless in his pursuit of technology solutions for our warfighters, rapidly accelerating delivery of mine resistant vehicles to our troops to protect them from improvised explosive devices in Iraq and Afghanistan,” Mr Biden said in a statement. “His work saved countless lives and limbs.”

Barack Obama said in a statement that he “relied on Ash’s strategic counsel as we invested in innovation and a stronger, smarter, more humane, and more effective military for the long term.”