Syria's military began large-scale exercises simulating defense against outside "aggression," the state-run news agency said Sunday … an apparent warning to other countries not to intervene in the country's crisis.

The exercise began Saturday with naval forces in a scenario where they repelled an attack from the sea, and will include air and ground forces over the next few days, SANA said. State TV broadcast footage of missiles being fired from launch vehicles and warships.

Ground, air and navy troops are participating in the exercises aiming "to test the combat preparedness of the army", according to the report. The agency said that the drills were part of an annual training plan.

Syria's navy fired live missiles from ships and helicopters over the weekend, state media said on Sunday, in an exercise aiming at showcasing its ability to "defend Syria's shores against any possible aggression".

Syrian television aired video of a variety of missiles being fired from launchers on land and from ships and showed the Syrian Defense Minister Dawud Abdallah Rahijia in attendance.

"Naval Forces conducted an operational live fire exercise on Saturday, using missiles launched from the sea and coast, helicopters and missile boats, simulating a scenario of repelling a sudden attack from the sea," Syrian news agency SANA said, adding maneuvers would continue for several days.

Opposition figures have been calling for a no-fly zone and NATO strikes against Syrian forces, similar to those carried out in Libya last year which enabled rebel ground forces to end the rule of Muammar Gadhafi.

But while Assad has faced sanctions and international condemnation over his crackdown on dissent which has left thousands dead, major Western and Arab powers have shied away from the idea of direct military action.

Meanwhile on Sunday, Syrian rebels used a tank for the first time in attacking government forces, in what the opposition said was a "very important" shift in tactics in the 16-month old conflict. Also Sunday, Syrian television aired video footage showing forces loyal to President Bashar Assad launching missiles from land and sea.

"The brigades of the (rebel) Military Revolutionary Council in the eastern region carried out the attack against an artillery camp with the use of a tank seized earlier from the regular army," said the opposition Syrian Observatory for Human Rights.

It reported "certain" casualties among the Syrian forces in the attack in the eastern town of Deir al-Zour.

At least 30 troops were captured in the raid, according to the London-based organization, which claimed that the rebels had also shot down an unmanned reconnaissance plane in the same area on Saturday.

Fighting has intensified in recent months between the rebels and troops loyal to Assad, with the opposition claiming to be in control of large parts of the country.

For the first time since the uprising began last year, a senior intelligence officer has defected from Assad's regime. Colonel Hassan Latuf, the officer in charge of one of the towns near Aleppo, abandoned Assad's forces on Saturday to join the rebels. Until now, the defections have mainly occurred among military officials.

At least 35 people were killed across Syria, on Sunday, according to the opposition. The deaths included at least nine government soldiers killed in clashes with rebels, said the Syrian Observatory for Human Rights.

The Syrian forces bombarding rebel areas in Deir al-Zour and Daraa in the south, said the organization.

News from Syria cannot be independently verified, as authorities are barring most foreign media from the restive areas.

The surge in violence came a day before the United Nations and Arab League envoy Annan was set to visit Damascus in a bid to salvage his peace mission. Annan is to discuss with Assad the crisis and the mission of UN observers who have been in the country since April, an official at the Syrian Foreign Ministry told DPA.

The 300-strong observing team last month suspended its activities due to the spike in violence in the country.

Annan has admitted failure of his efforts so far to end the unrest in Syria, where the opposition estimates that more than 16,000 people have been killed since the conflict started in March 2011.

In an interview with the French newspaper Le Monde published Saturday, Annan said he had been working for a peaceful and political solution in Syria, but "the evidence shows that we have not succeeded."

Annan's plan for peace in Syria was based on a ceasefire that has never held.