"A limited coalition force entered Aden and another force is on its way" to the southern port city, said the official who requested anonymity.
The Saudi-led coalition has been conducting an air war against the Huthi rebels and their allies since March 26 but this is the first reported ground deployment inside the country.
A leading member of the popular committees, a locally recruited militia loyal to exiled President Abedrabbo Mansour Hadi, told AFP that the force "will start helping us in fighting the (Shiite) Huthis and (former president Ali Abdullah) Saleh's forces".
Other militia commanders confirmed that a few dozen coalition soldiers, mostly Saudis and Emiratis of Yemeni origin, were on the ground in Aden.
The coalition declared an end to its Operation Decisive Storm on April 21, saying the campaign would enter a new phase dubbed Renewal of Hope focused on political efforts, aid deliveries and "fighting terrorism".
Coalition spokesman Brigadier General Ahmed Assiri had said repeatedly during the first phase that a ground intervention was on the table if needed.