Explosions have been heard in the south-eastern Ukrainian city of Mariupol, despite a ceasefire agreed by the government and pro-Russian rebels.

A BBC correspondent there says intense blasts from the eastern edges rippled across the city late on Saturday. The fighting subsided overnight.

Mariupol is seen by the rebels as a key city on the route to Crimea.

On Saturday, the Ukrainian and Russian presidents said the ceasefire in eastern Ukraine was "largely holding".

It was signed during talks between representatives of Ukraine, Russia, the Organization for Security and Co-operation in Europe (OSCE) and pro-Russia rebels in Belarus and came into effect at on Friday.

There were no reports of major fighting in the east for the first 24 hours, but by Saturday evening the BBC's Fergal Keane tweeted from Mariupol that shelling had resumed.

There were explosions on the eastern fringes of the city close to government checkpoints, he said, and duels between artillery on both sides.

A checkpoint held by Ukraine loyalists seemed to be on fire, according to AFP journalists close to the scene.

Our correspondent says it is too early to say what impact this will have on the ceasefire across the eastern region, but it does not bode well.

In another development, a new report by Amnesty International accuses all sides in the conflict of committing war crimes.

The human rights group said civilians had accused Ukrainian government troops of shelling their neighbourhoods indiscriminately.

Witnesses also said that separatist fighters had "abducted, tortured, and killed their neighbours". The report accused Russia of fuelling separatist crimes.

Some 2,600 people have died in fighting after pro-Russian rebels seized towns in Ukraine's eastern Donetsk and Luhansk regions in April - a month after Russia's annexation of the southern Crimean peninsula.

Russia has repeatedly denied accusations by Ukraine and the West that it has been sending regular troops into eastern Ukraine to help the rebels.

Ukraine's President Petro Poroshenko and his Russian counterpart Vladimir Putin spoke by phone on Saturday to discuss steps to make Friday's truce durable.

In a statement Mr Poroshenko said they had stressed the need "to maximise the involvement" of the OSCE in monitoring the truce.

The two leaders also discussed ways of co-operating in delivering humanitarian aid to the region.

For his part, President Putin said in a statement that an agreement was reached to "continue dialogue".

The spokesman for Ukraine's National Security and Defence Council, Andriy Lysenko, said earlier on Saturday that the rebels had fired 10 times on Ukrainian troops since the truce.

Unconfirmed reports also say a number of fighters from Ukraine's Aydar battalion were ambushed and killed after the ceasefire.

The rebel leader of the self-proclaimed Donetsk People's Republic, Aleksandr Zakharchenko, said the truce was "not being fully observed" and that rebels had been subjected to shelling in the town of Amvrosiyivka near Donetsk.

Also, the International Committee of the Red Cross (ICRC) said in a tweet that aid trucks on their way to Luhansk had been forced to turn back by shelling, without giving any further details.

A BBC crew that travelled to Donetsk airport on Saturday morning heard gunshots and small explosions but residents said the night had been quiet.

Meanwhile, Russia vowed to respond if the European Union imposed new sanctions over the Ukraine crisis.

The EU says the sanctions, targeting more Russian individuals, will be introduced on Monday but could be suspended if Russia withdraws troops from eastern Ukraine and observes the truce.

The Russian foreign ministry said the EU was "practically sending a signal of direct support to the 'party of war' in Kiev".

(BBC)