MEXICO CITY (Reuters) - Mexican President Andres Manuel Lopez Obrador urged authorities on Monday to look into a report accusing a top aide of financial impropriety, while calling it part of a media campaign aimed at bringing his administration into disrepute. Newspaper El Universal said Lopez Obrador’s private secretary Alejandro Esquer had hired shell companies in the 2018 presidential election campaign when Esquer was finance secretary of the ruling National Regeneration Movement party (MORENA). One of the companies the paper said Esquer had paid for campaign-related services was in September included in a list of firms found by federal tax authorities to lack the means to provide the services advertised in its receipts.