President Ali Abdullah Saleh's authoritarian grip on Yemen appeared to be slipping as he accepted an offer from the Saudi king to travel there for medical treatment for wounds suffered in a rocket attack on his compound.

A Saudi official, who asked not to be named, said: "He's just landed. He's here for medical treatment. We are the closest country and we have the capabilities."

Asked whether Saleh was stepping down, the official said only: "He's coming for medical treatment."

The reports of Saleh's journey to Saudi Arabia came amid speculation from Yemeni and western analysts that it was unlikely that he would be able to return to Yemen if he was forced to seek medical assistance abroad.

Saleh delivered an audio address on television to reassure supporters, but his voice sounded laboured and the address was made accompanied by an old photograph of him on the screen.

Analysts fear that a sudden departure by Saleh, after 33 years in power, would leave a political vacuum and create even deeper chaos in Yemen, where the government has already lost control of some outlying provinces and al-Qaida and other jihadists have appeared to exploit the political turmoil to move more freely.

A leaderless Yemen would place enormous pressure on Saudi Arabia, which has long played the role of kingmaker for its much smaller, and infinitely poorer, neighbour.

The offer of treatment came as it was confirmed that Saudi Arabia – which has been deeply shaken by the events of the Arab spring – had acted to negotiate a ceasefire between the rival factions in Yemen even as it was arranging for Saleh's evacuation.

There are fears that without Saleh, whose regime has been responsible for the deaths of hundreds of protesters and political opponents, the nascent civil war between rival factions could escalate further and splinter the fragile state that is home to one of al-Qaida's most active franchises.

Earlier yesterday, conflicting reports of his whereabouts and condition spread through the Middle East after officials and opposition tribal leaders reported that Saudi King Abdullah had mediated a ceasefire in the conflict.

The violence in the country grew out of pro-democracy protests that has turned into a power struggle between Saleh's ruling clique and his former allies in the Ahmar clan.

Sadeq al-Ahmar, the eldest of the Ahmar brothers, whose fighters have been battling Saleh's forces in the capital, confirmed that the Saudis had arranged a ceasefire, which he said he would respect.

The extent of the president's injuries has been a matter of intense speculation: when the rocket struck the mosque in his presidential compound, he was surrounded by senior officials and his bodyguards. Eleven guards died and five officials standing near the president were seriously wounded. They have already gone to Saudi Arabia for treatment.

King Abdullah intervened in the conflict after almost four months of largely peaceful protests against Saleh spun out of control into an increasingly bloody civil conflict.

Late last night, al-Ahmar, who is also the head of the Hashid confederation, accused Saleh's troops of not observing the ceasefire. He said that the president's forces had not withdrawn from their positions in the city but were instead reinforcing those positions.

"We are respecting what we agreed upon under the guidance of the Saudi monarch to stop the bloodshed of innocents and bring safety for citizens based on our desire to bring security and quiet back to the capital, which is living through a terrible nightmare that Saleh's regime has brought upon it," al-Ahmar said in a statement.

Inspired by uprisings in Egypt and Tunisia, protesters have been trying unsuccessfully since February to oust Saleh with a wave of peaceful demonstrations that have brought out hundreds of thousands daily in Sana'a and other cities. Now the crisis has transformed into a power struggle between two of Yemen's most powerful families: Saleh's, which dominates the security forces, and the al-Ahmar clan, which leads Yemen's strongest tribal confederation, known as the Hashid. The confederation is grouped around 10 tribes across the north.

Al-Ahmar announced the Hashid's support for the protest movement in March, and his fighters adhered to the movement's non-violence policy. But last week, Saleh's forces moved against al-Ahmar's fortress-like residence in Sana'a, and the tribe's fighters rose up in fury.

There were signs last night the ceasefire was already unravelling as the boom of artillery fire could be heard again near the al-Ahmar compound in the Hasaba neighbourhood in northern Sana'a, where the fighting has been concentrated in the past two weeks.