Three American airlines – Delta, United and American Airlines – have banned the shipment of big-game trophies on flights after the illegal killing of Cecil the lion in Zimbabwe.

They would no longer transport lion, rhinoceros, leopard, elephant or buffalo remains, the airlines announced.

The airlines have not, however, given official reasons for their announcements.

Delta flies direct to a number of African cities and was subjected to an online petition to ban such shipments.

American Airlines and United fly to fewer sub-Saharan cities than Delta, but United said in a tweet its decision to stop carrying trophies was “effective immediately”.

United spokesman Charles Hobart said: “We felt it made sense to do so.”

Cecil the lion was shot illegally in July by American dentist Walter Palmer of Minnesota. Zimbabwe is seeking his extradition and that of a doctor from Pennsylvania, named as Jan Casimir Seski, who is suspected of killing another lion in April.

Walter Palmer is believed to have paid about $50,000 to hunt Cecil, a major tourist attraction in Zimbabwe’s Hwange National Park.

He says he thought the hunt was legal and was unaware Cecil was protected, but the killing triggered a huge online backlash.

Delta would not answer questions from journalists as to why it made its decision on August 3, nor would it detail how many hunting trophies it has transported in recent years.

“Effective immediately, Delta will officially ban shipment of all lion, leopard, elephant, rhinoceros and buffalo trophies worldwide as freight,” Delta said in a brief statement.

Its announcement came as several other airlines indicated that they are – or soon will be – stopping the transport of all trophy-hunting kills.

As recently as May, Delta said it would continue to allow such shipments.