Ali Abdullah Saleh, the Yemeni president, has called for a truce and new negotiations on his return to Sanaa after three months, as deadly clashes between forces loyal to him and dissident tribesmen continued in the north of the capital.
"The president calls on all political and military parties to achieve a truce and a ceasefire," said a presidency official.
For Saleh, "there is no alternative to dialogue and negotiations to end the bloodshed and resolve the crisis", the official added.
Saleh had been recovering in Saudi Arabia since suffering injuries in a bomb blast at his presidential palace in the capital, Sanaa, on June 3.
"Ali Abdullah Saleh, president of the republic, returned this morning to the land of the nation safely after a trip for treatment in Riyadh that lasted more than three months," Yemen Television announced on Friday.
The United States called on Saleh to transfer power and hold presidential elections by the end of the year.
Jay Carney, the White House spokesman, said the Yemeni people have suffered enough and deserve a path toward a better future.
Fierce clashes continued all day between security forces loyal to Saleh and dissident tribesmen, killing 18 people in the north of the capital, according to an opposition statement cited by the AFP news agency.
"Eighteen people were killed and 56 wounded" in the fighting in the district of Al-Hasaba, north of Sanaa, said Al-Sahwa.net, the news website of Yemen's Islamist main opposition party, Al-Islah.
The international civic organisation, Avaaz, said that more than four million pro-democracy youths had gathered in Change Squares across the country. Protests were taking place in 17 of Yemen's 21 provinces, mainly Sanaa, Taiz, Aden, Hodieda, Baitha, and Dhammar provinces.
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Witnesses reported that after hearing news of Saleh's return, protesters camped in Sanaa's main square tried to break through army lines, but were fired upon by government troops. Three were injured.
Fresh clashes and thuds of mortars were also heard throughout the night and early morning in Sanaa and Taiz, Yemen's second biggest city, killing seven people.
Sanaa has been gripped by street battles and exchanges of shelling between the elite Republican Guards, led by Saleh's son, and tribesmen opposing Saleh as well as military units who had defected.
Nearly 100 people have been killed in Sanaa and elsewhere in Yemen since Sunday.
Jamal Benomar, the UN envoy to Yemen, said on Wednesday that the deteriorating security situation, and the reluctance of both sides to reach a political resolution, raises "the risk of civil war breaking out".
Mahjoob Zweiri, a professor at Qatar University, told Al Jazeera that Saleh has returned most probably to implement promised changes.
"It's unlikely to see Abdullah Saleh has gone back to Yemen without some sort of consultation with Riyadh and Washington," he said.
"It seems to me that there is a kind of desire to see a solution with the presence of Ali Abdullah Saleh in Sanaa."
The ongoing clashes in Yemen have stalled a Gulf Co-operation Council (GCC) initiative that would lead to Saleh stepping down and handing over all constitutional authorities to his deputy.
In return, he and his family would be granted immunity from prosecution.
Saleh has retained power despite eight months of protests in which tens of thousands have taken to the streets to demand an end to his 33-year rule.