SANAA, Yemen — Riot police fired shots in the air and used tear gas against thousands of government opponents who also clashed with supporters of Yemen's longtime ruler on what protest organizers billed as a nationwide “Friday of Rage.” At least four people were wounded.

Riots also flared overnight in the southern port of Aden, the country's second-largest city, with police shooting to death one demonstrator after cars and a local government building were set ablaze, officials said. Tens of thousands rallied in the southern city of Taiz, a hotbed of dissent.

It was the eighth straight day of protests in Yemen inspired by uprisings in Egypt and Tunisia. Demonstrators in the Arab world's poorest country are calling for the ouster of President Ali Abdullah Saleh who has ruled the country for 32 years.

Organizers using social media sites Facebook and Twitter in summoning people to the streets for the “Friday of Rage” following noon prayer, and tens of thousands responded in the major cities of Sanaa, Taiz and Aden.

BERLIN — A German prosecutor has opened a murder investigation against a key witness in John Demjanjuk's trial on allegations the man may have been involved in mass killings at the Nazis' Treblinka concentration camp.Munich prosecutor Hans-Joachim Lutz told The Associated Press today the probe is based on statements from former guards that Alex Nagorny, 94, took part in shootings at the camp in occupied Poland in 1941-42.In one statement obtained by the AP, former guard Ivan Knysh told Soviet authorities in 1948 that he remembered Nagorny from Treblinka, and that “from his statements to me I know that he participated in a shooting of 3,000 prisoners.”Lutz said he is waiting on information from Ukraine to determine whether any of the witnesses are still alive to be cross-examined about their original statements before moving ahead with possible charges.

BEIJING — A hospital in southern China says surgeons have successfully removed a rusty, 4-inch knife from the skull of a man who said it had been stuck there for four years.An official at Yuxi City People's Hospital in Yunnan Province said Friday that Li Fuyan, a 30-year-old man, had been suffering severe headaches, bad breath and breathing difficulties but never knew the cause of his discomfort.The official says Li told doctors he had been stabbed in the lower right jaw by a robber four years ago and the blade broke off inside his head without him realizing it.

LONDON — Kate Middleton's fashion choices have been in the spotlight ever since her engagement to Prince William. Now, a famous frock from Middleton's university years may be the hottest item at an auction — just weeks before the royal wedding.The see-through dress Middleton modeled in 2002 at a charity fashion show at Scotland's St. Andrews University will go up for sale at Kerry Taylor Auctions in March. The knitted mesh slip was designed in 2000 by Charlotte Todd, who was then a fashion and textile design student at the University of the West of England.The piece was part of Todd's project titled “The Art of Seduction.”“I'd like to call myself a royal matchmaker,” Todd, 31, told The Associated Press. “It's definitely a showstopping dress. I'd like to think I played my part in history and in fashion history.”