At least one protester was killed and more than 20 others injured when riot police dispersed demonstrations demanding the ouster of the regime in Yemen's business capital Aden on Friday, the day which saw the most massive rallies ever in several cities in the aftermath of the Tunisian and Egyptian uprisings.

Tens of thousands took to the streets in various Aden districts, with the biggest rally held in Al-Mansoura district, and the protesters chanting anti-government slogans including those calling for the removal of the Saleh regime.

Riot police broke up rallies in some districts, firing on the demonstrators killing Muhammad Saleh, who got a shot in his head, and injuring many others, eyewitnesses said. Arrests also took place, specifically in Al-Arish district, the eyewitnesses said.

Security has been tightened in Aden and the police are preventing the people from leaving their areas, as if there was a state of emergency declared.

Amid the crackdown protesters burned the municipal authority building in Al-Mansoura after they forced the police who opened fire on them out of the building.

In some the protests continued peacefully.

Today, more than half a million people gathered at Sana'a University, the square of change, for prayers and to show their support and blessing to the popular sit-in there.

They demanded Saleh to resign before the next Friday the day the sit-inners will march on the presidential palace.

Preacher Sa'ater who delivered the sermon criticized the attempts of the regime to incite regionalism among the people, saying such attempts will only lead to further alignment and unity of the people, not what the regime is really seeking.

The blood of those who were killed while protesting in Sana'a and other cities will not go in vain, however, these martyrs will be the fuel of a true revolution against the oppressive and corrupt regime, he preached.

In Tahrir Square, thousands of pro-government protesters gathered to show their support to President Saleh and his regime.

Plus, hundreds of thousands of people flooded to the square of freedom in Taiz, where the people have been on a sit-in protest for weeks, and to squares in Hodeida, Ibb, Saada and other cities demanding the departure of Saleh as the anti-government protests continue to escalate throughout Yemen.

The preachers who delivered Friday's sermons urged the regime to learn from the Tunisian and Egyptian lessons, saying the mass rallies were a clear message to the ruler to implement concrete political and economic reforms before the country is dragged into an unacceptable situation.