Fighting between Yemen's government forces and security units loyal to the Southern Transitional Council (STC) intensified on Friday as loud explosions rocked different parts the southern port city of Aden.

The STC's security forces engaged in intense armed confrontations with Saudi-backed Yemeni government forces around the country's Presidential Palace in Crater neighborhood of Aden, according to local residents near the scene.

A military official told Xinhua that heavy weapons including tanks were used in the fighting raging for the control of presidential palace amid loud explosions that shook the ground.

The STC forces besieged the palace from different directions and continued in advancing in the surrounding areas amid heavy clashes with Presidential Guard forces, he said anonymously.

"Several high-ranking government officials left the palace one day ago and some officials are now positioned inside their residential building elsewhere in Aden," said the source.

Many families in Crater neighborhood of Aden are stranded due to the escalating fighting between the two warring rivals in their area, where the Presidential Palace is located.

Residents spoke to Xinhua by phone saying that they were unable to get out to buy food or medicine as armored vehicles surround their houses and called for a safe corridor.

Other security sources told Xinhua that non-stop armed confrontations are taking place since Thursday night around the residential building of the country's Interior Minister, Ahmed Maisry in Aden's neighborhood of Mansourah.

The fighting started when senior leaders of the STC accused the Saudi-backed Yemeni government of "backing Islamists and leaking information to the Iranian-backed Houthis" who targeted an army base in Aden last week, killing scores of soldiers including commanders.

The STC threatened "to seize the presidential palace and expel all the member of the Saudi-backed Yemeni government who are linked to Muslim Brotherhood parties," despite the rejection of the Saudi-led coalition for the calls of violence in Aden.

The Saudi-backed Yemeni government issued a statement and held the STC full responsibility for destabilizing the situation in Aden and fomenting sedition in the country's southern regions.

On Wednesday, the UN Special Envoy to Yemen Martin Griffiths expressed deep concerns over a military escalation in Aden and called on the parties involved to abandon violence and engage in dialogue to resolve differences.

"I am alarmed by the military escalations in Aden, including reports of clashes in the vicinity of the presidential palace. I am also deeply concerned by the recent rhetoric encouraging violence against Yemeni institutions," he said in a statement.

"Escalations of violence will contribute to instability and suffering in Aden and will deepen Yemen's political and social divisions," he said.

Considered Yemen's temporary capital, Aden is where the Saudi-backed Yemeni government has based itself since 2015.

The impoverished Arab country has been locked in a civil war since late 2014, when Houthi rebels overran much of the country and seized all northern provinces, including the capital Sanaa.