DONETSK Ukraine (Reuters) - Artillery shells hit close to the centre of Ukraine's separatist-held city of Donetsk for the first time on Thursday, killing at least one person, as a large Russian aid convoy rumbled towards the border.

With Ukrainian government forces tightening the noose on pro-Russian separatists, shelling rocked Donetsk, sending frightened residents rushing for cover, witnesses said.

It was not immediately clear if the artillery was fired by government or rebel forces.

Two shells landed 200 metres (660 feet) from the Park Inn Radisson, one of the city's main hotels, shattering windows. The blasts opened up a yawning hole on the third floor of an apartment block and left a broad crater on the pavement.

Nearby, a body covered by a sheet lay stretched out on the blood-stained ground.

A huge Russian convoy carrying 2,000 tonnes of water, baby food and other humanitarian aid drove through southern Russia towards the frontier, while Kiev repeated it could not enter until Ukrainian authorities had cleared its cargo.

The caravan of 280 trucks left the Moscow region on Tuesday, looking to take aid to Luhansk region, in eastern Ukraine, where the main city is held by the separatists.

The pro-Western Kiev government says the humanitarian crisis is partly of Moscow's making and has denounced the dispatch of aid as an act of cynicism. It is also fearful that the operation could become a covert military intervention by Moscow to prop up the rebels who appear on the verge of defeat.

Moscow, which denies charges - also voiced by the West - of arming the rebels with tanks, missiles and other heavy military equipment, has dismissed as "absurd" suggestions it could use the convoy as a cover for invasion.

In Geneva, a spokeswoman for the International Committee of the Red Cross, which would be responsible for distributing the aid in Ukraine, said: "The question of border crossing procedures and customs clearance (for the convoy) still have to be clarified between the two sides."

A senior Ukrainian presidential aide said that the Russian cargo could be taken into the country only under the auspices of the Red Cross and on completion of all border formalities.

"Ukraine will not allow onto its territory any accompanying escort for the cargo and any repetition of attempts to send in so-called peacekeepers," said the aide, Valery Chaly.


BORDER DOUBTS

Reuters journalists following the convoy said on Thursday it was heading south from the city of Voronezh towards Rostov-on-Don and was no longer seeking entry through Ukraine's Kharkiv region as had first been assumed.

Ukrainian authorities had indicated that they did not want the convoy moving through the government-controlled north-east rim, apparently concerned it might provoke trouble.

The question now was whether the trucks would head for one of the many parts of the border under rebel control on the Ukrainian side - something which would make checks by Ukrainian border authorities difficult, if not impossible.

"If decisions are taken to bring the humanitarian aid in through areas of the border which are temporarily under the control of the terrorists, the cargo will all the same have to be looked at by Ukrainian border guards and transferred to representatives of the Red Cross," said military spokesman Andriy Lysenko on Thursday.

It was not immediately clear how this could happen.

Relief agencies say people living in Luhansk and in Donetsk, the region's main industrial hub, are facing shortages of water, food and electricity after four-months of conflict in which the United Nations say more than 2,000 people have been killed.

In Donetsk, people poured out of their offices into the stairwell of the city's main administration building after loud explosions nearby triggered an evacuation warning.

A short while later, the whistling sound of incoming shells were swiftly followed by at least two further blasts.

Liliya Chelina, 54, lived in the apartment block whose wall was smashed by a projectile. "It came straight into the apartment. Thank God I was not in the kitchen," she said.

"My husband promised me that shells would never hit our house, only large buildings. But look at what has happened."

A woman called Tamara, who showed a deputy's card for the self-proclaimed Donetsk People's Republic, said she believed the separatist fighters had fired the shells. "One of the fighters said they had done it," she said.

The separatist Internet news outlet Novorossiya said Ukrainian government forces hit targets in the Leninsky region of Donetsk and have struck regions to the east and southwest of the city in previous days.

The news outlet said hardest hit areas were Makiyivka's Hirnitsky neighbourhood as well as areas between Donetsk and Dokuchaevsk which lies south of the city.

Ukrainian troops have been slowly encircling Donetsk, the regional hub with a peace-time population of nearly a million.


(Additional reporting by Maxim Shemetov and Dmitry Madorsky, southern Russia; Writing by Richard Balmforth; Editing by Crispian Balmer)