Damascus: Aleppo, the largest city of Syria is in “dire” state witnessing a fierce battle, involving fighter aircrafts being used by the government forces on rebels, said the UN mission in Syria on Wednesday.

Aleppo, a city of 2.5 million, has been mired in a severe conflict since last 12 days, when the Syrian military launched a huge crackdown in order to retake the areas captures by the rebels.

The Syrian military has been using heavy weapons, tanks, helicopters and warplanes to fire upon the rebels.

The rebels on the other hand are seen giving a tough competition to Assad’s forces as now, even they possess heavy weapons of their own, including tanks, said Sausan Ghosheh, the spokeswoman for the UN mission in Syria.

"Yesterday, for the first time, our observers saw firing from a fighter aircraft. We also now have confirmation that the opposition is in a position of having heavy weapons, including tanks," she said.

She described “heavy use of heavy weapons, including tanks, helicopters, heavy machine guns, as well as artillery.”

Meanwhile Syrian President Bashar al-Assad motivated his military to step up their offensive against “a multi-faceted enemy with clear goals.”

On the occasion of the 67th anniversary of the Army, Assad sought to enthuse his Army, saying, “Today you are invited to increase your readiness and willingness for the armed forces to be the shield, wall and fortress of our nation”.

This battle will determine the destiny of our people and the nation's past, present and future, added Assad.

Assad has not spoken in public since a bomb on July 18 killed four of his top security officials during a rebel assault on Damascus.

Syria's powerful military, which has largely held together over the course of the uprising, is vital to keeping Assad in power. The pace of defections has been rising recently, however. Neighboring Turkey reports that 28 generals have already crossed the border.

The UN mission in Syria says that the civil war in Syria is escalating and there is shortage of food, fuel, water and gas.

Amidst heavy firing and gunshots, several in the embattled Syrian city of Aleppo have escaped but many are trapped as they find it “dangerous” to flee the city, a UN official said.

Thousands in Aleppo have been compelled to seek refuge in schools, mosques and public buildings, but there are others who haven't fled the city as they haven't had the means, said Melissa Fleming, spokeswoman for the UN High Commissioner for Refugees (UNHCR).