Long-held aspirations for autonomy in south Yemen erupted into deadly conflict between separatists and unionist supporters of the government in 2017-18 and again last August, complicating Yemen's wider war.

The separatists, who unilaterally declared self-rule in April, on Wednesday moved to mend the rift, withdrawing the proclamation and pledging to implement a Saudi-brokered peace agreement with the government which had stalled last year.

Here is a recap of tensions in the south:

Unification
South Yemen was an independent country from 1967, when British colonial forces withdrew paving the way for the creation of a Soviet-backed communist one-party state, until 1990, when it united with the north.

An attempt to break away again in 1994 sparks a brief civil war that ended with northern troops and their militia allies occupying the south.

Government retreats to south
In September 2014, northern-based Huthi rebels complete their takeover of the capital Sanaa and much of the north, prompting President Abedrabbo Mansour Hadi to flee to second city Aden, the former southern capital.

Saudi Arabia forms a military coalition to prop up Hadi's forces.

Rival administration
In April 2017, Hadi sacks Aden governor Aidarous al-Zoubeidi, a supporter of autonomy for the formerly independent south.

Thousands of Aden residents demonstrate.

In an open challenge to Hadi, Zoubeidi in May launches a parallel authority to administer the southern provinces, the Southern Transitional Council (STC).

Aden palace siege
In January 2018 a separatist force dominated by STC supporters seizes almost all of Aden and surrounds the presidential palace, sparking three days of clashes in which 38 people are killed.

The group, called the Security Belt Forces, is backed by the United Arab Emirates (UAE), a key member of the Saudi-led coalition aiding Hadi against the Huthi rebellion.

After coalition mediation, the separatists lift the siege of Aden.

Clashes erupt
New clashes between Security Belt and pro-government forces break out in Aden in August 2019.

The separatists gain ground across the city, saying they have seized the presidential palace. Four days of fighting leaves 40 dead and 260 wounded, according to the United Nations.

STC supporters vacate some public buildings in Aden but keep hold of military positions after Saudi and the UAE send in mediators.

Separatists in control
In late August, Hadi's forces enter Aden and announce they are in "full control", including of the presidential palace, but are forced to withdraw the next day as the separatists retake the city.

Hadi's government accuses the UAE of launching air strikes against its troops in support of separatist fighters, reportedly leaving dozens dead. The UAE confirms the strikes, but says it had targeted "terrorist militias" in self-defence.

Saudi warning, talks
In September, Saudi Arabia demands separatists return captured military and civilian facilities. The kingdom calls for dialogue but insists there is "no alternative to the legitimate government".

Hadi's government publicly rules out talks at first, but it emerges on October 7 that the two sides are holding indirect negotiations through Saudi mediators.

Short-lived deal
On October 14, the UAE hands over to Saudi forces key positions in Aden, including an airbase and the international airport, in a bid to defuse tensions between separatists and the government.

A power-sharing deal is signed in Riyadh on November 5, handing the STC a number of government ministries and allowing the government to return to Aden.

But that agreement quickly unravels, as deadlines for forming a new cabinet with equal representation for southerners and the reorganisation of military forces go unimplemented.

On April 26, the STC declares self-rule for the south.

Deal revived
On July 29, the STC announces it is "abandoning its self-rule declaration" to allow implementation of the Riyadh Agreement, acknowledging that Saudi Arabia and the UAE had experted pressure to row back on the proclamation.

Riyadh said it had proposed a plan to "accelerate" implementation of the agreement, with the Yemeni prime minister to form a new government within 30 days among other measures.