President Pervez Musharraf has imposed a state of emergency in Pakistan because of mounting militant attacks and "interference" by members of the judiciary.
Those were the reasons cited in the presidential order. Troops are now surrounding the state television station and the Supreme Court. The constitution has been suspended, senior judges arrested, and all telephone lines inside the country cut off.
The US says its extremely disturbed by the situation and had urged Musharraf to give up his army uniform.
The president made his move as Supreme Court judges were set to rule on whether his re-election last month was legal, given he was still army chief.
A new chief justice has now been appointed.
Pakistan's police and military personnel have been attacked on numerous fronts in a wave of fundamentalist violence in recent months, but Western governments urged Musharraf not to do anything which would threaten a return to full democracy.
The state of emergency is expected to delay the parliamentary elections planned for January 2008 by up to 12 months.