Yemen's President Ali Abdullah Saleh has returned to the country from Saudi Arabia three months after surviving an assassination attempt, officials say.
Yemen TV said President Saleh arrived in the capital, Sanaa, by private plane at dawn. No other details were given.
He went to Saudi Arabia in June for treatment following a rocket attack on the grounds of the presidential palace.
President Saleh, who has been in power for more than 30 years, has faced months of protests urging him to quit.
Correspondents say his return raises the risk of all-out civil war.
"We're definitely going to have an escalation of violence, but let him come back - we want him to come back and be tried for his crimes," said protest organiser Mohammed al-Asl.
Activists have been camped out in an area of Sanaa dubbed Change Square since January demanding an end to his rule.
Clashes in the capital have recently intensified as elite Republican Guards, led by President Saleh's son Ahmed, fight running battles with army units that have defected to the opposition and tribal fighters who support the protesters.
More than 80 people, mostly unarmed protesters, have been killed since Sunday.
Medics say at least one person was killed overnight and many others wounded when mortars landed in Change Square. Other reports said four people were killed in the northern al-Hasaba district on Friday.
'Critical escalation'
Correspondents in Sanaa reported a surge in artillery and machine-gun fire as news of President Saleh's return broke. As least some of the gunfire was celebratory, they said.
Yemeni state TV broadcast old footage of Mr Saleh and played national songs as it reported his return.
The Yemeni embassy in Washington confirmed President Saleh had returned.
In Sanaa, anti-government protesters and supporters of President Saleh are expected to hold rallies after Friday prayers.
"His return means more divisions, more escalation and confrontations," protest leader Abdel-Hadi al-Azizi told AP news agency.
"We are in a very critical escalation."
Hopes of a lasting ceasefire between the sides, to enable a reform process to take place in which President Saleh would yield power, are fading.
On Tuesday the government agreed a truce following negotiations with Western envoys. However, the ceasefire broke down hours later.
The UN High Commissioner for Human Rights, Navi Pillay, warned on Thursday that Yemen was at a "dangerous crossroads".
Gulf Co-operation Council (GCC) chief Abdulatif al-Zayani visited Yemen on Tuesday to try to broker a deal to the crisis but left the next day empty-handed.
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9/23/11
Yemen President Ali Abdullah Saleh returns to Sanaa
4:15 PM
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