* Saleh arrives in Saudi Arabia for medical treatment
* PM's aide says former president is source of tension
Yemen's ousted president arrived in Saudi Arabia on Tuesday for medical tests, and a government official said he should stay in exile as his presence provoked separatists and rebels in a nation struggling to regain stability.
Ali Abdullah Saleh, who stepped down in a Gulf-brokered deal in 2012 after a year of protests against his rule, remains influential in the impoverished Arab country. Gulf neighbours and Western nations fear the wily leader's continuing sway may tip a delicate political transition into chaos.
Restoring stability in Yemen has become a priority for the United States and its Gulf allies concerned about al Qaeda-linked militants active in a country neighbouring top oil exporter Saudi Arabia and lying on major world shipping lanes.
Yemeni sources said pressure had been mounting on Saleh to go abroad to ease political tensions, particularly after his announcement that he would head his party, the General People's Congress (GPC), in a national dialogue which started last month.
Ali al-Sarari, an aide to Prime Minister Mohammed Basindwa, said Saleh's presence had irritated southern separatists, Shi'ite Muslim Houthi rebels and young activists behind the uprising that helped end the veteran president's 33-year rule.
"Saleh's departure is a cause of relief and his presence (in Yemen) is a source of much worry because he was behind much of the actions that created tension," Sarari told Reuters.
"His departure for medical treatment must be followed with an isolation from political life and a prevention from having any influence in political life," he added.
Saudi officials were not immediately available for comment.
The 69-year-old Saleh, who remains secretary-general of the GPC, had long been expected to travel abroad for more treatment for wounds sustained in a bomb attack in 2011.
But his party's website said he had pushed back his planned departure for Riyadh until after the opening on March 18 of national reconciliation talks, which he did not attend.
For decades, Washington and Riyadh saw Saleh as an ally who could contain Islamist militants operating in Yemen. His ruling party has half the seats in the transitional cabinet.
In December President Abd-Rabbu Mansour Hadi ordered a broad overhaul of the military. He abolished the elite Republican Guard, led by Saleh's son, Brigadier-General Ahmed Saleh, as well as the First Armoured Division, commanded by General Ali Mohsen al-Ahmar, who had sided with Saleh's opponents.