The Pakistan supreme court has set up a judicial commission to investigate a secret memo scandal that threatens the federal government.
Friday's decision deals a blow to ruling party politicians who have argued that such an inquiry is unnecessary, lawyers say.
These politicians have suggested that the government's opponents on the supreme court, in the army and in the political opposition are using the scandal as a way to topple the country's leadership.
The government had argued that a court investigation was unnecessary because parliament was the more appropriate forum and was already looking into the matter.
The scandal centres on a memo allegedly sent in May to Admiral Mike Mullen, chairman of the US joint chiefs of staff at the time, asking for help in stopping a supposed army coup following the Navy Seals raid in May that killed Osama bin Laden, the al-Qaeda chief.
The scandal first erupted in October when Mansoor Ijaz, a US businessman of Pakistani origin, wrote a column in the Financial Times newspaper claiming that Husain Haqqani, the US ambassador in Washington, drafted the memo and asked him to send it.
Ijaz also claimed the memo had the support of Asif Ali Zardari, the Pakistan president.
Both Haqqani and Zardari have denied the allegations, but Haqqani resigned afterwards under pressure.
Pressure on government
The army, which has denied it ever intended to carry out a coup, was outraged by the memo and supported the supreme court's investigation.
Speaking to Al Jazeera, Mubashir Zaidi, editor of Pakistan's Dawn TV, said the judiciary's move will increase the pressure on the civilian government, led by Zardari's Pakistan People's Party.
"By this judgement, the supreme court has set a tone to put further pressure on the government, as the government has to comply with the court's orders," he said.
Asma Jahangir, Haqqani's defence lawyer, discusses the supreme court ruling in interview to Al Jazeera
"The government now needs to come up with a concrete strategy to deal with this properly."
The court's order, which calls for setting a three-judge commission to investigate the memo scandal, came in response to a petition filed by a group of opposition politicians, including the opposition leader and former prime minister, Nawaz Sharif.
The panel will be led by the chief justice of the Balochistan high court, Qazi Faez Eisa, and must deliver its report within four weeks, Zafar Ullah, Sharif's lawyer, said.
"We should have trust and confidence in this commission," Ishaq Dar, a member of Sharif's political party and another one of the petitioners, said.
On the opposite side, Haqqani's lawyer, Asma Jehangir, said after the supreme court ruling: "This is the most disappointing judgment. National security has been given priority over human rights."
There is longstanding tension between Pakistan's military and its civilian leadership because the army has staged a series of coups and ruled the country for much of its 64-year history.
The political crisis comes at a time when Pakistan is facing a violent Taliban campaign, a faltering economy and troubled relations with its most important ally, the US.