Thousands of people rallied outside Egypt's defence ministry Friday calling for the military rulers' ouster a day before a civil disobedience campaign marking Hosni Mubarak's overthrow a year ago.

The military responded by saying it would not bow to threats or plots against the state, official television reported.

During the day, several groups of protesters converged near the ministry as the security forces blocked off access with barbed wire and tanks.

Military music blared from behind the barrier, while the activists chanted slogans such as: "The people want the execution of the Field Marshal" -- Hussein Tantawi, head of the ruling military council since Mubarak's ouster.

The activists set off from several points across Cairo and snaked through residential areas to bypass military cordons several kilometres (miles) from the military headquarters.

The protesters plan a day of strikes and sit-ins to mark the anniversary on Saturday.

"We will never yield to threats, and we will never give in to pressure," the much-criticised Supreme Council of the Armed Forces said in a statement broadcast by state television.

The SCAF also said Egypt was the target of conspiracies aiming to sow instability.

"We tell you quite frankly that our dear Egypt faces plans aimed at striking at the heart of our revolution," the statement said.

"We are facing plots against the nation aiming to undermine the institutions of the Egyptian state, and to topple the state itself so that chaos reigns."

After Friday's main weekly Muslim prayers, protesters at the Fateh mosque in central Cairo began chanting "Down with military rule!" before setting off on their march.

"We are marching to the defence ministry, we want to remove the military," said prominent activist Asmaa Mahfuz, who taped an influential video more than a year ago calling on Egyptians to rise up against Mubarak.

Young activists such as Mahfuz, whom the military had threatened to put on trial after she attacked the ruling generals in Internet postings, have turned their sights on the army a year after toppling Mubarak in an 18-day uprising.

The military, which promises to hand over power after a president is elected later this year, said it would deploy troops across the country, state media reported.

The threatened civil disobedience campaign has divided the country's political forces, with the Muslim Brotherhood -- the big winner in recent parliamentary elections -- coming out against it.

Students in several universities have called for strikes on Saturday, with secular youth groups who spearheaded the revolt against Mubarak joining in.

Tareq al-Khouly, an organiser of the April 6 youth group, said the plan was for a one-day strike, which could be extended.

In a joint statement on Friday, the groups called on Egyptians "to support these strikes in order to end the unjust rule and build a nation in which justice, freedom and dignity prevail."

Although the military was initially idolised for not siding with Mubarak during the uprising, it has since faced growing protests against its continued rule and has several times used deadly force to disperse demonstrations.