Saudi King Abdullah will undergo new back surgery in Riyadh in the next few days, following two similar operations last year in the United States, the palace said in a statement on Tuesday.
Exams performed after the 87-year-old king complained of "pain in the lower back" revealed a stretched ligament, said the statement quoted by the Spa official news agency.
"The operation will be carried out in the next few days in Riyadh," it said.
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King Abdullah flew to New York on November 22 and was operated on two days later for a debilitating herniated disc complicated by a haematoma that put pressure on his spine.
That surgery was declared a success, as was a second operation to repair several vertebrae and Abdullah returned to Saudi Arabia on February 23.
The monarch's advanced age combined with health problems have raised concerns about the future of Saudi Arabia, which has been ruled by the Al-Saud family since 1932.
Abdullah's half-brother, Crown Prince Sultan bin Abdul Aziz, who has held the post of defence minister ever since 1962, is 83 and has been slowed by what is believed to be cancer.
Prince Nayef, 77, third in line to the Saudi throne, was appointed second deputy prime minister in March 2009.