The Arabic television channel Al Jazeera has broadcast what it says is a message from Osama Bin Laden, in which he hails as "heroic" last week's attacks on US Marines in Kuwait and on a French supertanker off Yemen. The statement - which Al Jazeera says bears Osama Bin Laden's signature - also urged Muslims to unite against Americans and Jews. No-one has been able to confirm the authenticity of this or previous Bin Laden messages broadcast by Al Jazeera, a Qatar-based satellite channel. There is also widespread speculation about whether the Saudi-born militant is still alive.