With Saudi Arabia actively participating in the anti-ISIS coalition, security is reportedly extremely high as this year's hajj is set to begin tomorrow. With 1.3 million visas already granted, total pilgrimage numbers may approach 2 million, though reportedly Saudi security has already blocked 100,000 prospective pilgrims. Concerns are high that sympathizers of ISIS or other radical groups might cause trouble.
In the years after the Iranian Revolution, Iranian pilgrims frequently chanted slogans during the hajj, and in 1987 this erupted into full-scale violence, leaving hundreds dead according to Iran. Saudi Arabia disputed those numbers. Clearly the Saudis are eager to avoid a repetition of the 1987 events.
More on this year's hajj as it proceeds. You can watch live streaming of the hajj here.