At least one person killed as fighting between southern separatists and government troops continues for second day.

Fighting between southern separatists and presidential guards in Aden, the seat of Yemen‘s internationally-recognised government, has continued for a second straight day, raising concerns about the opening up of a new front in the country’s long-running war.

Sounds of gunfire echoed through the southern port city on Thursday while smoke and fire could be seen rising from the Jebel Hadid area, part of the Crater district that houses the hilltop presidential palace, witnesses and residents told Reuters news agency.

Local sources told Al Jazeera the clashes spread to adjacent streets and neighbourhoods where tanks and heavy weaponry were used.

A man was killed when a stray bullet hit him while he was walking in the street, his relatives said, a day after fighting between the separatists and the government troops killed several people, according to reports.

The violence is exposing a rift within a Saudi-led military coalition battling the Houthi rebel movement, in a devastating war that has killed tens of thousands of people since 2015 and pushed Yemen to the brink of famine.

It could also cause tensions between Saudi Arabia and the United Arab Emirates (UAE), which is part of the Saudi-led coalition but is believed to be backing the secessionist movement.

Civilians ‘trapped’

The separatists and the internationally-recognised government of President Abd-Rabbu Mansour Hadi are nominally united in their battle against the Houthis, but they have rival agendas for Yemen’s future. The separatists have also accused a Hadi-allied party of complicity in a Houthi missile attack last week on their soldiers.

Relations between Hadi and the UAE have been tense amid allegations the Emiratis have offered patronage to southern Yemeni politicians campaigning for secession, as well as what Hadi perceives as UAE’s violations of his country’s sovereignty.

Aden is the temporary home of Hadi’s government, though he is in Saudi Arabia and the presidential palace is largely empty apart from soldiers.

Ahmed Maher, a Yemeni journalist based in Aden, told Al Jazeera the confrontations between the presidential guards and the so-called Security Belt forces have negatively affected the lives of Aden’s residents, who have become “trapped”.

“The Crater district is a predominantly residential one,” Maher said. “Residents currently cannot access clinics, hospitals, markets, or schools – so we expect to see many civilian casualties if the clashes are prolonged.”

According to Maher, part of the reason the UAE-backed Security Belt forces are seeking to capture this area is because it is the “highest point in Aden”.

“If they capture the palace and its vicinity, they would be able to easily target any of the city’s neighbourhoods from the Jebel Hadid hilltop,” he said, adding that the Security Belt forces are well-equipped with weapons and vehicles.

“We have not yet seen the same level of mobilisation attempted by the Yemeni presidential guards,” he said.

UN de-escalation call

Clashes first erupted on Wednesday after the funeral of those killed in the missile attack on a military parade in Aden last week.

Following the funeral, Hani Ali Brik, the vice president of the separatist Southern Transitional Council which is affiliated with the Security Belt forces, had reportedly called on supporters to march to the palace and overthrow the government.

On Thursday, a senior official in Hadi’s embattled government accused Brik of “fomenting sedition”. In a statement carried by the official news agency, Minister of Interior Ahmed al-Maisari called on Brik’s supporters to ignore his calls, saying “they only aim at engendering war” and undermine the fight against the Houthis.

The latest surge in violence prompted a United Nations call for de-escalation.

“I am alarmed by the military escalations in Aden,” the UN’s special envoy for Yemen, Martin Griffiths, said in a statement on Wednesday.

“I am also deeply concerned by the recent rhetoric encouraging violence against Yemeni institutions,” he added.

The Saudi-led alliance condemned the fighting and said it plays into the hands of the Houthis.

UAE troop withdrawal

The UAE began withdrawing several thousand troops from Yemen last month in a move that weakens the Saudi-led coalition, signalling differences between the two close allies over how far to pursue the war against the Houthis.

The UAE will still have an estimated 90,000 allied fighters in the coalition-held south, ensuring its continued influence and potentially posing a threat to the Saudi-backed government.

Saudi Arabia has not commented on the troop withdrawal but has adopted a much harder line towards the separatists than it did after a similar eruption of violence in January 2018, when southern forces took control after two days of fighting, confining Hadi’s government to the presidential palace.

Yemen’s latest conflict broke out in late 2014 when the Houthis, allied with forces loyal to former President Ali Abdullah Saleh, seized much of the country, including Sanaa.

The war escalated in March 2015 when the Saudi-led coalition launched a ferocious air campaign against the rebels in a bid to restore Hadi’s government.

Since then, tens of thousands of civilians and combatants have been killed and as many as 85,000 children may have starved to death.