Dozens of Arab special forces soldiers arrived in the Yemeni port city of Aden on Sunday to bolster the anti-Houthi forces amid a fierce offensive by the Shia rebels and their allies, sources have told Al Jazeera.

Saudi Arabia denied that a ground operation was under way by the anti-Houthi coalition it leads, but declined to comment on Sunday on the presence of special forces - a topic Riyadh has consistently refused to address in the more than one-month-old conflict.

In Aden, Ali al-Ahmadi, the spokesman for the Southern Popular Resistance, a group defending the southern port city against an advance by the Iranian-allied Houthis, told Reuters news agency that the fighters battling the rebels around Aden airport are Yemenis, not Arab special forces troops deployed by the Saudi-led coalition.

A Saudi spokesperson has also issued a denial. He confirmed, however, that the Arab coalition remained engaged in the fight in the Arabian Peninsula nation.

"There are no foreign forces in Aden but coalition continues to help fight against the Houthi militia," Brigadier General Ahmed al-Asiri said in a statement.

Peter Salisbury, an analyst and journalist who has lived in Yemen, said he had been told the soldiers "are Yemeni but they have been trained abroad and will coordinate more closely with the coalition".

Saudi Arabia, Iran and the 'Great Game' in Yemen

Sources had told Al Jazeera that 40 to 50 special forces troops had been sent to Aden to help pro-government forces.

"The local fighters don't have access to the kind of weapons they have been seen with," Al Jazeera's Mohamed Vall, who is reporting from Riyadh, said.

"Saudi Arabia has repeatedly suggested that there could be a ground invasion but appeared optimistic there would not be the need."

The coalition, which seeks to restore the government of President Abd-Rabbu Mansour Hadi, includes eight other Arab states and is receiving logistical support from the United States, Britain and France.

It has refused to rule out the eventual use of ground troops, but to date it has mostly used air power and some artillery on the Saudi border to bombard Houthi militia and allied army units.

Anti-Houthi hotbed

Aden, a hotbed of anti-Houthi sentiment, has been a flashpoint since the war began on March 26, when the coalition began attacking Houthi forces opposed to Saudi-backed Hadi, who was based in Aden for several weeks before fleeing to Riyadh.

Fighting around Yemen has killed more than 1,000 people, including an estimated 551 civilians since the bombings started, the United Nations said on April 24. Its children's agency UNICEF said at least 115 children were among the dead.

The United Nations has also warned of an imminent collapse of infrastructure in the country due to a major fuel shortage.