UNITED NATIONS—An environmental advocacy group says in a report released Thursday that over 1.4 million rosewood logs from Nigeria worth $300 million were illegally sent to China after Nigeria’s then-Environment Minister Amina Mohamed signed thousands of retroactive permits. U.N. spokesman Stephane Dujarric said Mohamed, who is now the U.N. deputy secretary-general, “rejects any allegations of fraud.” …Since 2013, the Washington-based Environmental Investigation Agency said, Nigeria has been transformed from a net importer to the world’s largest exporter of rosewood logs, which is causing desertification, threatening national parks and imperiling the livelihoods of millions of people.