Oman has stripped an exiled former Yemeni vice-president of his citizenship for intervening in his home country's politics.
Ali Salem al-Beed, who fled from Yemen in 1994 after a civil war erupted there, lost his right to stay in the Sultanate of Oman on Friday.
He violated the conditions of his citizenship in calling on residents of south Yemen to fight for liberation, the Omani authorities said.
Al-Beed, whose attempt to secede from north failed in 1994, said in Germany on Friday that the international community should force the Yemeni government to withdraw its army from the south.
There were clashes in Yemen on Thursday over the country's 1990 unification - part of ongoing protests that have threatened to reopen the country's old north-south divide.
At least four people died in the violence, which broke out in the capital Aden a day before the anniversary of the union - one marked by unity celebrations, political speeches and military parades.
A security official in Aden said police shot into the air to disperse the crowd, but did not confirm or deny any deaths or injuries.
He emphasised that the protest had not been officially approved. The protests are reportedly being organised by the Southern Movement, a loose coalition of groups opposed to the government in Sanaa, the capital.
Protesters sang independence songs, highlighting the depth of separatist sentiment in the south where living conditions are worse than in the rest of the country.
But in his anniversary-day address, Ali Abdullah Saleh, the Yemeni president, gave warning that those who want to secede would fail as they did in 1994.
He said the country's unity was "solid and blamed "outlaws" for the violence, which he said aimed "to hit at the nation and its safety and to stir unrest".
Saleh has cautioned in the past against the risk of Yemen splitting into "several entities". In addition to the southern unrest, Yemen's government also faces the risk of a potential rebellion by Shia Zaidi Muslims living in the north.
Saleh announced during his speech that his government had plans to change the constitution and develop the political and electoral system so as to grant more power to provincial rule in an effort to attract investment.
Southern Yemen is home to four million people, whereas the north's population is more than 20 million. For decades southerners have complained of jobs and land being reserved for the northerners.