Saudi Arabia has warned it would use “all means” to ensure a peaceful hajj pilgrimage amid turmoil in other Arab countries and rising tension with Iran.

Crown Prince Nayef bin Abdel Aziz, new heir to Saudi King Abdullah, said Tuesday the kingdom is “ready to face events peacefully” but would meet those “who want to attack” with all means necessary.

More than 1.5 million Muslims have already arrived in Saudi Arabia for the annual event, which begins on Friday. Hajj rituals will peak on Saturday. Most pilgrims come early to visit the holy mosques in Mecca and nearby Medina, where the prophet Mohammed was buried over 1,400 years ago.

Saudi Arabia has avoided the protests which have swept across the Arab world this year, toppling leaders in Tunisia, Egypt and Libya and leading to violent uprisings in Syria, Yemen and Bahrain.

King Abdullah instead has offered support to allies who faced popular revolts and averted any similar protests inside the kingdom with a ban on demonstrations and spending billions of dollars on housing and other social benefits.

Already strained ties between Iran and the Saudi kingdom worsened last month when the U.S. said two Iranians had plotted to assassinate the Saudi ambassador to Washington with support from Tehran.

In 1987, clashes between Iranian pilgrims and Saudi security forces led to the deaths of hundreds of people.

The hajj is one of the five pillars of Islam – one which every Muslim must fulfill, if possible, during his or her lifetime.