The man whom U.S. authorities most want to capture or kill, al-Qaida leader Osama bin Laden, has turned 50, if the reclusive terrorist is still alive.

Birthday messages from purported followers have appeared on militant Web sites offering the al-Qaida leader prayers for a long and healthy life. Bin Laden was born in 1957 in Saudi Arabia, although his exact birthdate remains a mystery.

The most recent video footage of him dates back to 2004, and that has fueled speculation that the terrorist leader might be in poor health or even dead.

He is wanted in connection with the September 11, 2001, terrorist attacks on the United States that killed nearly 3,000 people. The U.S. government is offering a $25 million reward for his capture.

In a speech on the fifth anniversary of the 2001 terrorist attacks, President Bush said the U.S. will find and bring Osama bin Laden to justice, no matter how long it takes.

Earlier this year, the fugitive leader of Afghanistan's ousted Taleban regime, Mullah Mohammad Omar, said he has not seen bin Laden since late 2001.

Some information for this report provided by AP and Reuters.