SHARJAH, UNITED ARAB EMIRATES, JUNE 17 -- State radio said today that Sharjah's ruler has abdicated because of "financial difficulties," but reports in neighboring sheikdoms said he was ousted in a palace coup.

Sheik Sultan bin Mohammed Qassimi, 48, was in London at the time.

Sharjah radio broadcast an abdication statement, purportedly on Sultan's behalf, saying he was transferring power to Sheik Abdel-Aziz, 50, who is his brother and the military commander.

Soldiers took up positions at Sharjah's squares and key intersections. Sharjah has a population of about 210,000 and is the richest and third-largest of the seven United Arab Emirates sheikdoms at the southern end of the Persian Gulf.

Oil was discovered in Sharjah in 1972. Its shipments of about 60,000 barrels a day of gas condensate make up about 50 percent of the UAE's total exports.

The UAE, formed in 1971, consists of Abu Dhabi, Dubai, Sharjah, Ajman, Fujairah, Umm Quwain and Ras Khaimah. Abu Dhabi is the seat of the federated government.

Arab diplomatic sources and airport officials in Dubai, nine miles away, said later that Sultan had arrived there by air from London.

Sheik Zayed bin Sultan Nahyan, president of the UAE, summoned the federation's seven-man Supreme Council to an emergency meeting in Abu Dhabi.

"That fact that guardsmen loyal to Abdel-Aziz were stationed at important places shows that Sultan was overthrown," an Arab diplomat in Abu Dhabi said privately.

Troops cordoned off Government Square, the palace and nearby government buildings. Witnesses said soldiers seized the offices of Sharjah's radical Al Khaleej newspaper.

Shortly before sundown, the official UAE news agency WAM distributed a statement saying Sultan cited "financial problems" and "accumulating debts" in abdicating after 15 years of ruling his state.

Dubai's radio, however, said Sultan's fall from power "is an unacceptable move to take over government by force."

Dubai's radio called Sultan "the legitimate ruler" of Sharjah and its leaders urged the federation government to intervene immediately. "Security of the federation is indivisible, and basic procedures of succession are of concern to all," it said. "The situation should be handled with decisiveness and firmness."

Later, the official UAE news agency said notables of Sharjah's ruling Qassimi clan had met and sworn allegiance to Abdel-Aziz.

Western diplomats in Abu Dhabi said Sultan has been criticized for economic mismanagement and frequent trips abroad. Last year's fall in oil prices hit Sharjah heavily and forced it to borrow an estimated $1 billion.