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Donald Trump's sons are facing more scrutiny for their African hunting expedition that recently came to light.

The trip is currently the subject of an investigation led by conservationists in Zimbabwe.

Donald Trump Jr., who stars on " The Celebrity Apprentice" alongside his dad, and his brother Eric sparked outrage among animal lovers on Twitter earlier this month after photos surfaced of the two posing with animals they killed during a 2011 safari trip in Africa. Trump Jr. later defended their actions in part by tweeting, "I'm a hunter, for that I make no apologies."

Donald Trump Jr. on safari (Huntinglegends.com via Flickr)

Trump Jr. may be a hunter, but TMZ.com reports the independent Zimbabwe Conservation Task Force says the South African safari company the sons used was not registered in Zimbabwe.

The task force says Trump Jr. and his brother killed an elephant, a buffalo and a crocodile, among other animals. In one of the leaked pictures, Trump Jr., is seen holding a knife and the cut-off tail of an elephant.

The group is investigating whether license and trophy fees were paid.