By Angus McDowall
BEIRUT (Reuters) - Lebanese Prime Minister Saad al-Hariri visited the United Arab Emirates on Tuesday, his first trip outside Saudi Arabia, as regional tensions aggravated by his surprise resignation escalated into a domestic crisis.
Hariri, an ally of Saudi Arabia, flew to Abu Dhabi and then returned to Riyadh, his office said. His Future TV channel said he would also visit Bahrain.
His resignation has thrust Lebanon back into the frontline of a Middle East rivalry pitting a mostly Sunni bloc led by Saudi Arabia and allied Gulf monarchies against Shi'ite Iran and its allies.
On Monday, Saudi Arabia accused Lebanon of declaring war against it because of aggression by Iran's Lebanese ally Hezbollah, dramatically escalating the crisis and threatening to destabilise Lebanon.
Lebanese politicians and Hezbollah were on Tuesday silent about the escalation in Saudi rhetoric after a series of consultations with President Michel Aoun, a Hezbollah ally.
A rocket fired from Yemen was intercepted on the outskirts of Riyadh hours after Hariri's resignation on Saturday. On Monday, Saudi Foreign Minister Adel al-Jubeir told CNN the rocket "was an Iranian missile launched by Hezbollah".
Hariri's resignation collapses a national unity government agreed last year in a political deal that united Lebanon's opposing sides and led to the country's first budget since 2005 and agreement on a new law for parliamentary elections, which could be derailed by the crisis.
Aoun has said he will not accept Hariri's resignation until he returns to Lebanon to explain his thinking -- a move widely seen as a stalling tactic.
Hezbollah and its allies will struggle to form a government without Hariri or his blessing. The post of prime minister must be filled by a member of Lebanon's Sunni community, among which he is the most influential politician.
Lebanon's dollar bonds fell and the cost of insuring exposure to its debt jumped on Tuesday in response to the crisis, and the ratings agency Moody warned of damage to its credit rating.
The finance minister, central bank governor and head of the banking association all issued statements on Monday stressing Lebanon's financial and monetary stability.
The sudden nature of Hariri's resignation has also fuelled speculation in Lebanon that he was coerced into quitting and has been held against his will. Saudi Arabia and Hariri's political allies have denied this.
The pro-Hezbollah al-Akhbar daily reported that he "was placed under house arrest hours after arriving in Riyadh last Friday", that a Saudi security team was supervising his movements and that he had only limited access to his phones.
Fouad Siniora, a former prime minister and member of Hariri's Future Movement, said he had spoken to him on Monday and added that Hariri would return to Lebanon.
(Reporting by Angus McDowall, Ellen Francis, Tom Perry and Lisa Barrington, Editing by Angus MacSwan)