Barack Obama is travelling with a 27-strong delegation to cement ties with the new king of Saudi Arabia on Tuesday as concerns over Yemen and the Islamic State take centre stage in the increasingly volatile region. Central Intelligence Agency director John Brennan, Republican hawk senator John McCain and General Lloyd Austin, head of US Central Command forces in the region, are among the surprise additions to a hastily organised trip that has drawn critical comparisons with the US failure to send any senior figures to Paris following recent terrorist attacks.