Islamabad: Pakistan's Supreme Court opened hearings on Monday into a secret memo sent to Washington that has sharply raised tensions between the powerful military and the civilian government.

The proceedings could hurt President Asif Ali Zardari politically and further enflame relations between the government and the military, which was outraged by the letter asking for Washington's help in reining in the army in exchange for a raft of policies favorable to the United States.

Last week, the army chief and the country's spy chief called for an investigation into the affair in statements to the Supreme Court.

That triggered speculation about the future of Zardari, who was receiving medical treatment in Dubai for what one associate said was a "mini stroke."

The president returned to Pakistan early on Monday. The Supreme Court is acting on 11 petitions, including one filed by the country's opposition leader calling for an investigation into the memo.

The petitions allege the country's envoy to Washington, Husain Haqqani, masterminded the letter, and have sought the judiciary's intervention to determine whether he acted alone or with the backing of Zardari's government. Haqqani, a key ally of the president, resigned late last month under army pressure.

A nine-judge panel was hearing the petitions Monday, but it was unclear what action the court would take. It could dismiss the petitions, order the government to investigate the affair or pronounce some form of judgment itself. That could happen later Monday or in the weeks or months to come.

The army has ruled Pakistan directly or indirectly for most of the country's existence. It still wields immense domestic political power despite being under the nominal control of the government.

The Supreme Court, considered relatively hostile to Zardari, is also a major power center. Political commentators have speculated that the army, which has been on the defensive since the May 2 US raid that killed Osama Bin Laden in a Pakistani garrison town, is using the memo scandal to weaken Zardari.

However, they also say the military has no appetite to oust the president, not least because they don't want direct "ownership" of the country's massive economic and social problems.

Over the weekend, Prime Minister Yousuf Reza Gilani said there was no clash between the army and the government, leading some to suggest that Zardari, a canny political operator who has survived several other predictions of his demise, may have worked out a behind-the-scenes-deal with the army. The president flew to Dubai on December 6 amid confusion over his health and reason for leaving.

Officials released a statement by his doctor last week saying Zardari, who has a heart condition, had lost consciousness for several minutes and was suffering from pain in his arm. One associate has said privately that the president suffered a "mini-stroke" that had left no lasting affects.