FIFA President Sepp Blatter has called for unity in a speech to delegates as they prepare to vote on the presidency of football's world governing body. The run-up to the vote has been dominated by mounting allegations of corruption surrounding FIFA. Seven senior officials were arrested at a hotel in Switzerland on Wednesday. Mr Blatter, who is expected to win a fifth term, appealing to unity and team spirit. He said those targeted by investigations, carried out by the US and Swiss authorities, were not the entire organisation. Mr Blatter has been called on to quit but has already made clear he is not responsible for the scandal and wants to combat corruption. In another development, the UK's Serious Fraud Office says it is actively assessing material in its possession relating to FIFA corruption allegations. FIFA's 209 members will vote in the coming hours in a secret ballot on whether to give Mr Blatter, 79, a fifth four-year term as president. The only challenger is Prince Ali bin al-Hussein of Jordan, 39.