* Scud-type missiles increasingly used on residential areas
* Rebel mortars land near presidential compound
* Russia says war crimes request unconstructive
* Typhoid breaks out in opposition areas
By Khaled Yacoub Oweis
AMMAN, Feb 19 (Reuters) - A Syrian missile killed at least 20 people in a rebel-held district of Aleppo on Tuesday, opposition activists said, as the army turns to longer-range weapons after losing bases in the country's second-largest city.
The use of what opposition activists said was a large missile of the same type as Russian-made Scuds against an Aleppo residential district came after rebels overran army bases over the past two months from which troops had fired artillery.
As the uprising against President Bashar al-Assad, now a civil war, nears its two-year mark, rebels also landed three mortar bombs in the rarely-used presidential palace compound in the capital Damascus, opposition activists said on Tuesday.
The United Nations estimates 70,000 people have been killed in the conflict between largely Sunni Muslim rebels and Assad's supporters among his minority Alawite sect. An international diplomatic deadlock has prevented intervention, as the war worsens sectarian tensions throughout the Middle East.
A Russian official said on Tuesday that Moscow, which is a long-time ally of Damascus, would not immediately back U.N. investigators' calls for some Syrian leaders to face the International Criminal Court for war crimes.
Moscow has blocked three U.N. Security Council resolutions that would have increased pressure on Assad.
Casualties are not only being caused directly by fighting, but also by disruption to infrastructure and Syria's economy.
An estimated 2,500 people in a rebel-held area of northeastern Deir al-Zor province have been infected with typhoid, which causes diarrhoea and can be fatal, due to drinking contaminated water from the Euphrates River, the World Health Organization (WHO) said on Tuesday.
"There is not enough fuel or electricity to run the pumps so people drink water from the Euphrates which is contaminated, probably with sewage," the WHO representative in Syria, Elisabeth Hoff, told Reuters by telephone.
The WHO had no confirmed reports of deaths so far.
BURIED UNDER RUBBLE
In northern Aleppo, opposition activists said 25 people were missing under rubble of three buildings hit by a several-metre-long missile. They said remains of the weapon showed it to be a Scud-type missile of the type government forces increasingly use in Aleppo and in Deir a-Zor.
NATO said in December Assad's forces fired Scud-type missiles. It did not specify where they landed but said their deployment was an act of desperation.
Bodies were being gradually dug up, Mohammad Nour, an activist, said by phone from Aleppo.
"Some, including children, have died in hospitals," he said.
Video footage showed dozens of people scouring for victims and inspecting damage. A body was pulled from under collapsed concrete. At a nearby hospital, a baby said to have been dug out from wreckage was shown dying in the hands of doctors.
Reuters could not independently verify the reports.
Opposition activists also reported fighting near the town of Nabak on the Damascus-Homs highway, another route vital for supplying forces in the capital loyal to Assad, whose family has ruled Syria since the 1960s.
Rebels moved anti-aircraft guns into the eastern Damascus district of Jobar, adjacent to the city centre, as they seek to secure recent gains, an activist said.
"The rebels moved truck-mounted anti-aircraft guns to Jobar and are now firing at warplanes rocketing the district," said Damascus activist Moaz al-Shami.
Russian Deputy Foreign Minister Gennady Gatilov told a news conference a U.N. war crimes report, which accuses military leaders and rebels of terrorising civilians, was "not the path we should follow ... at this stage it would be untimely and unconstructive."
Syria is not party to the Rome Statute that established the ICC and the only way the court can investigate the situation is if it receives a referral from the Security Council, where Moscow is a permanent member. (Writing by Oliver Holmes; Editing by Jason Webb)