DAMASCUS, Syria: Two mortars exploded near one of Syrian President Bashar Assad's palaces in Damascus on Tuesday but caused only material damage, Syria's state news service said.

The attack was the first confirmed strike close to a presidential palace and another sign that the civil war is seeping into areas once considered safe

and reaching closer to the heart of Assad's seat of power in the capital.

The news service, SANA, said "terrorists" fired the rounds that struck near the southern wall of the Tishreen palace in the capital's northwestern Muhajireen district. The government rebels to anti-government fighters as "terrorists."

No casualties were reported and it was unclear whether Assad was in the palace. He has two others in the city.

Assad often uses the Tishrin palace to receive dignitaries and as a guest house for foreign officials during their visits to Syria.

His two other palaces are the People's Palace on Qasioun mountain overlooking the capital and Rawda palace in the central neighborhood of Abu Rummaneh.

For security reasons, Assad movements are shrouded in secrecy and it is unclear how much time he spends in any of the palaces. His public appearances have grown increasingly infrequent as the civil war has spread.

The Syrian capital has largely been spared the violence that has left other Syrian cities in ruins. For weeks, however, rebels who have established footholds in the suburbs have been pushing closer to the heart of the city from the eastern and southern outskirts, clashing with government forces.

Rebels have claimed to fire rockets at the presidential palaces before, but Tuesday's strike was the first confirmed by the government.

In the northern city of Aleppo, a Syrian missile strike leveled a stretch of buildings and killed at least 19 people, leaving residents combing through the rubble to find those trapped beneath it, anti-regime activists said Tuesday.

The strike was the latest salvo in a fierce and bloody 7-month battle for Syria's largest city and economic center, a key prize in the civil war.

Rebels have slowly expanded their control over parts of Aleppo since first storming it last summer. The city is now divided between rebel- and regime-controlled zones.

Rebel forces have been trying for weeks to capture the city's international airport and two military airbases nearby, while the government is bringing in reinforcements from areas it still controls further south and regularly bombing rebel areas from the air.

The Britain-based activist group the Syrian Observatory for Human Rights said 31 people were confirmed dead in the attack late Monday night, including 14 children and five women.

The activist Aleppo Media Center said more than 40 were killed and published the names of 21 off them on its Facebook page. There was no way to reconcile the differing tolls.

Both groups said the strike appeared to be from a ground-to-ground missile. The Syrian government did not comment.

Activist Mohammed al-Khatib of the AMC said via Skype that the death toll could rise further as residents search the site for more bodies.

"There are still many martyrs under the rubble. ... There are still lots of people missing from the area," he said.

He said the strike appeared to be from a large ground-to-ground missile because of the scale of the destruction and because residents did not report hearing a fighter jet, as they usually do during airstrikes.

Videos posted online showed scores of men searching the destroyed buildings in the poor Jabal Badro neighborhood for the dead and wounded. One man swung a sledgehammer to break through concrete while a bulldozer hauled off rubble. In another video, a man covered in grey dust struggled under pile of concrete.

The videos appeared authentic and corresponded with other Associated Press reporting.

Although President Bashar Assad's forces regularly shell and launch airstrikes on areas held by anti-government rebels, their use of large missiles has been limited.

In December, U.S. and NATO officials confirmed rebel reports that Syrian forces had fired Scud missiles at rebel areas in northern Syria. That was the last confirmed use of such weapons.

Also Wednesday, rebels clashed with government forces near Aleppo's international airport and the Kweiras military airport nearby, the Observatory said.

Clashes have halted air traffic to the two airports for weeks, since rebels launched their offensive to try to capture them.

The Observatory also reported government shelling and airstrikes and clashes between government forces and rebels east and south of the capital, Damascus. Seven people were killed in rocket strikes on the eastern suburb of Kafar Batna and five died in a car bombing in Jdeidat al-Fadel, southwest off the capital, it said.

The Syrian state news agency said the army had carried out "successful operations against terrorists" in Aleppo, mentioning a number of neighborhoods that did not include Jabal Badro.

Syria refers to rebels seeking to topple Assad as "terrorists" and blames the conflict on an international conspiracy to weaken the country.

The U.N. says some 70,000 have been killed since Syria's uprising against Assad's rule began in March 2011.

The violence has spread humanitarian suffering across much of Syria.

The U.N. warned in a report released Monday that contaminated water and poor hygiene practices in populated areas have led to an increase in waterborne diseases such as Hepatitis A and Typhoid.

The World Health Organization said the health situation on the ground is rapidly deteriorating, with an estimated 2,500 people in the northeastern Deir el-Zour province infected with Typhoid and 14,000 cases of Leishmania, a parasite responsible for an infectious and often debilitating disease, in Hassakeh province.

It also said Hepatitis A has been reported in Aleppo and Idlib and some crowded shelters hosting displaced people in Damascus.

International diplomacy has failed to stop the violence. The U.S. and other Arab and European countries have called on Assad to stand down, while Russia, China and Iran continue to back him. Russia, Syria's largest arms supplies for decades, has said it will continue to fulfill its arms contracts with Assad's regime.

Russia on Tuesday said it had sent two jets carrying humanitarian aid to Syria and are inviting Russians who want to leave the country to take the flights back.

The Emergency Situations Ministry on Tuesday said the two planes had already left Moscow for northwestern port of Latakia, carrying 40 tons of aid, including portable power generators, blankets, canned food and sugar. It says Russians are welcome to fly back on the planes.

Russia's defense ministry also said it would deploy four ships in the Mediterranean but did not connect this to the situation in Syria. Russian news agencies quoted unnamed officials as saying the ships would be present in case Russia needs to evacuate its citizens.

In January, Russia flew 77 of its citizens out of Syria on two flights from Beirut. The foreign ministry says it is not planning a large-scale evacuation.