DONETSK, Ukraine (AP) -- Shelling in at least three cities in eastern Ukraine has hit a home for the elderly, a school and multiple homes, adding to a rapidly growing civilian death toll Tuesday.
The use of unguided rockets in fighting between government troops and pro-Russian separatist rebels has been causing a notable increase in casualties in recent days and drawn criticism from the U.N. and rights groups.
And with turmoil raging across a swathe of Ukraine's troubled east, international investigators were again prevented Tuesday from visiting the site of the Malaysia Airlines jet shot down earlier this month.
At least one person was killed when several shells hit an apartment block in early in the afternoon in the center of the main separatist rebel stronghold of Donetsk.
The government has refrained to date from attacks on the center of Donetsk and direct strikes on the city may mark an escalation in efforts to break the rebels' resolve there.
An Associated Press reporter on the scene saw gaping holes in the side of a nine-story apartment block after it was fired on. Around 50 people took refuge in a nearby underground car park and the area was heavy with the smell of household gas.
An international observer team was taking photos of another nearby building that was also struck by rocket fire.
City hall in Luhansk, which is also controlled by separatist rebels, said that five people were killed Monday when a home for the elderly was struck by artillery fire. Russian television showed images of bodies in wheelchairs covered with blankets.
Ukraine security spokesman Andriy Lysenko said that rebels had blocked the railroad out of Luhansk, barring residents from leaving the city.
"If we were earlier able to organize additional trains to and from Luhansk, to Kiev, now they have completely blocked the railway line," Lysenko said.
Lysenko also accused separatist fighters of using children as human shields and stopping cars from leaving Luhansk. It was not immediately possible to confirm those claims.
In Horlivka, a city besieged by government troops, the mayor's office reported Tuesday that 17 people, including three children, were killed as a result of shelling.
The mayor's office said there has been major damage to many homes and government offices in the center of the city. It also said the top floor of a school was destroyed as a result of direct hit from a shell.
Rebels accuse the government of indiscriminately using heavy artillery against residential neighborhoods in areas under their control.
A U.N. monitoring mission in Ukraine says there has been an alarming buildup of heavy weaponry in civilian areas of Donetsk and Luhansk - including artillery, tanks, rockets and missiles that are being used to inflict increasing casualties and damage to civilian infrastructure.
The U.N. said in a report this week that use of such weaponry could amount to a violation of international humanitarian law.
"There is an increase in the use of heavy weaponry in areas that are basically surrounded by public buildings," said Gianni Magazzeni, head of the U.N. office's branch that oversees Ukraine. "All international law needs to be applied and fully respected."
Ukraine's government has stated that it has banned use of artillery in heavily resided areas and in turn accuses separatists of targeting civilians in an effort to discredit the army.
The U.N. report acknowledged the government's promise not to bombard the cities of Donetsk and Luhansk. However, it said that "people trapped in areas controlled by the armed groups continue to be killed as the heavy shelling continues from both sides. Questions arise about the conformity of these attacks with the rules governing the conduct of hostilities."
The U.N. called for a "full and impartial investigation" of all incidents where civilians have been killed.
New York-based Human Rights Watch has been more categorical in its accusations against the government and last week produced what it said was evidence the army had fired on houses in the suburbs of Donetsk.
The overall death toll has been steadily rising. The U.N. has said that at least 1,129 people were killed between mid-April, when fighting began, and July 26.
Ukrainian troops have for several days encroached on the outskirts of Horlivka, which is just north of the regional center and the main rebel stronghold, Donetsk.
Heavy fighting has also spread to other areas in the region, including towns not far from the crash site of Malaysia Airlines Flight 17.
Lysenko said Tuesday that 10 soldiers were killed and another 55 wounded in fighting over the past day.
A team of Dutch and Australian police officers and forensic experts is currently stationed in Donetsk in the hope of traveling to the fields where the Boeing 777 came down.
For the third day running, the delegation has been forced to cancel plans to travel to the area of the wreckage.
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