Riad Farid Hijab, the Syrian prime minister, has announced through his spokesman that he is joining the opposition, after state television reported that he was sacked this morning.
The former prime minister arrived in Jordan after being smuggled across the border, Jordanian authorities confirmed to Al Jazeera on Monday.
"I announce today my defection from the killing and terrorist regime and I announce that I have joined the ranks of the freedom and dignity revolution. I announce that I am from today a soldier in this blessed revolution," Hijab said in a statement read in his name by spokesman Muhammad el-Etri.
Etri also denied that Hijab had been sacked, saying that the government had made the announcement of his dismissal after officials realised that the prime minister had fled the country.
Etri said that the defection was planned "for months", and was executed in conjunction with the Free Syrian Army.
The former prime minister encouraged other Syrian officials to defect in the wake of his announcement, Etri said, adding that with his departure other, less senior, officials "have no excuse not to defect".
Hijab has accused President Bashar al-Assad of carrying out "genocide" against his own people, prompting Washington to say the regime was "crumbling".
US acting State Department deputy spokesman Patrick Ventrell welcomed the recent desertions, which he said also included Syria's first cosmonaut and a senior intelligence officer.
He said the defections "indicate that the regime is crumbling and losing its grip on power".
Heading to Qatar
Hijab's spokesman cautioned, however, that the Syrian government was likely to "react haphazardly, in a hysterical manner. It will perpetrate more killings [and] any official willing to defect must act wisely. He must take care of himself and his family".
"The regime speaks only one language: the language of blood," Etri told Al Jazeera.
Hijab is to leave Jordan for Qatar within days, following the example of other high-profile defectors, Etri told AFP news agency.
"Hijab will go to Doha, where international media are based. He will leave for Qatar tomorrow, the day after or after a few days," he said in the Jordanian capital.
A member of the Syrian opposition in Jordan said Hijab will travel to Qatar "in the coming few hours".
"We are currently co-ordinating to facilitate the departure of Hijab to Doha in the coming few hours, most probably at 2200 GMT. Seven of his brothers will stay in Jordan," he told AFP, saying he had helped Hijab defect.
"We understand the sensitivity of this issue for Jordan. We do not want to create problems for the kingdom, which already has tense relations with the Syrian regime," he said, on condition of anonymity.
Given 'no choice'
President Bashar al-Assad appointed Hijab, a former agriculture minister, on June 23, following a parliamentary election in May.
Etri claimed that the former PM had not been given a choice, however, when appointed to the post.
"This defection has been being planned for more than two months. He was given two options: to either take the office of prime minister or be killed. He had a third option in mind: to plan his own defection in order to direct a blow to the regime from within and today he is declaring his defection," he told Al Jazeera.
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"I believe he is the highest ranking official in Syria [to defect]... it is one of a kind and it will have grave repercussions on the regime and significant implication after the departure of the regime and [for] the success of the revolution."
Omar Ghaliwanji, Syria's deputy prime minister, has been chosen to lead a caretaker government, state media reported on Monday.
Authorities hailed the May poll as being a major step towards political reform, but the opposition movement against Assad's government dismissed them as a sham.
Hijab had been a part of the Baath party command since 1998, and was appointed as the head of the Latakia governorate when anti-government protests first broke out there last year.
Al Jazeera's Rula Amin, reporting from Beirut in neighbouring Lebanon, said that while Hijab was not a key member of Assad's inner circle, were he to join the opposition he would be the most high-profile official to have rejected Assad's authority.
George Jabbour, a past adviser to former Syrian President Hafez al-Assad, told Al Jazeera that the development was "certainly significant".