But Yemeni government and militia forces said several dozen troops had landed in the main southern city, with some sources saying they were to assist in fighting for its international airport.
An AFP journalist saw several men in the vicinity of the airport dressed in military-style clothing, wearing helmets and carrying sophisticated weaponry.
"A limited coalition force entered Aden and another force is on its way" to the port city, a Yemeni government official in Aden told AFP, requesting anonymity.
The coalition launched air strikes against the Iran-backed Shia Huthi rebels and their allies on March 26 after they seized control of large parts of the country and advanced on Aden, where President Abedrabbo Mansour Hadi had taken refuge.
Fighting for airport
A leading member of the so-called "popular committees" militia supporting Hadi told AFP the newly deployed troops "will start helping us in fighting the Huthis and Saleh's forces".
The troops will mainly back pro-Hadi fighters around the rebel-held airport, which has changed hands several times and was again the focus of heavy fighting on Saturday night, he said.
Other militia commanders confirmed that a few dozen coalition soldiers, mostly Saudis and Emiratis of Yemeni origin, were on the ground in Aden. One militia source said some 30 soldiers from coalition countries had deployed to "supervise" operations to retake the airport.
Coalition spokesman Brigadier General Ahmed Assiri denied a major ground force had landed in Aden.
"I can assure you that no (coalition) forces disembarked on the ground in Aden today," he told Saudi news agency Al-Ekhbariya.
But in comments to Doha-based Al-Jazeera television, Assiri said that "all options are open".
"The coalition leadership will not spare any effort to support the resistance and achieve positive results on the ground," Assiri said.
On Sunday, coalition warplanes pounded rebel positions in and around the airport as clashes raged on, said a pro-Hadi military official.
Medics in Aden said that at least 18 people, most of them civilians, were killed since Saturday and 65 others wounded.
Local officials said most of the casualties resulted from rebel mortar shelling and gunfire across residential areas.
The coalition declared an end to its Operation Decisive Storm air strikes on April 21, saying the campaign would enter a new phase dubbed Renewal of Hope focused on political efforts, aid deliveries and "fighting terrorism".
But air strikes have continued and the coalition has faced increasing criticism for its campaign. At least 1,200 people have been killed in Yemen since late March and thousands more have been wounded.
Accusations of cluster bombs
Countries that have joined the coalition include the Gulf Arab monarchies, Egypt, Sudan and Morocco.
Moroccan King Mohammed VI visited Saudi Arabia Sunday and discussed "regional and international developments" with King Salman, the official SPA news agency reported.