Saudi King Abdullah, who has just returned to the kingdom after a month-long absence, has launched a huge expansion project for the Prophet's mosque in the holy city of Medina, the state news agency reported. The expansion project, expected to be the largest of its kind, is set to begin after the annual Muslim pilgrimage, the hajj, at the end of October, the SPA news agency reported late on Monday. According to Saudi officials, the project will require the expropriation of lands that could cost the government some $6.6 billion in compensation. Once completed, the three-phase project will mean the mosque will be able to  accommodate an added 1.6 million worshippers. Its current capacity is 200,000. The total cost of the project has not been released. King Abdullah laid the foundation stone for the expansion project after flying in from Morocco where he has spent the past month. The 88-year-old monarch is a frequent visitor to Morocco where his family owns palaces in Casablanca, the economic capital, and Agadir to the southwest. King Abdullah left the new heir to the throne, Crown Prince Salman bin Abdul Aziz, who is also deputy prime minister and defence minister, in charge of the oil-rich kingdom during his absence, SPA reported. It was the first time the king had travelled abroad since he appointed Salman, 76, first in line to the throne in June following the death of crown prince Nayef ben Abdel Aziz at the age of 79.