One soldier has reportedly been killed and another eight wounded in fresh separatist attacks in eastern Ukraine, according to Ukraine's military.

The report of Thursday's fatality came as the OSCE security watchdog gave warning of a "worrisome" spread of violence in the region.

The fighting has lessened significantly since a ceasefire between Ukrainian forces and Russian-backed rebels was declared in mid-February, but both sides accuse the other of violations and casualties are reported almost daily.

"Fighting has not died down along a broad stretch of the frontline from Krasnogorivka to Svitlodarsk,"  Oleksander Motuzyanyk, Ukrainian military spokesperson, said on Thursday, referring to government-controlled villages to the west and northeast of rebel-held Donetsk city.

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"The enemy is actively using heavy weapons ... The area of fighting is expanding," he said.

Motuzyanyk did not say whether this was the location where the soldier was killed.

For his part, Eduard Basurin, a senior separatist commander, accused government troops of wounding two rebel fighters and two civilians in attacks on rebel territory in the past 24 hours, according to DAN, a separatist press service.

Motuzyanyk's assessment of a spread in fighting has been backed by Alexander Hug, deputy chief of the OSCE's monitoring mission in Ukraine.

"Worrisome is that the geographical scope of the conflict seems to be spreading," Hug said in his weekly report on the situation in the east.

The rebellion by Russian-backed separatists in Ukraine's industrialised east has created the biggest crisis in relations between Russia and the West since the end of the Cold War.

The West and Ukraine say there is "incontrovertible proof" that Russia is providing men and weapons to the separatists - something Russia denies.

'Incontroversible proof'

Under the terms of the ceasefire agreement, brokered by Ukraine, Russia, Germany and France to end the conflict which has killed over 6,200 since last April, both sides should have withdrawn large-calibre weapons and tanks from the frontline.

The OSCE mission monitors weapons-holding areas in territory controlled by Kiev and by the rebels to make sure both sides are sticking to the terms of the truce.

This week, "in many of them, previously recorded weapons are now missing despite claims that withdrawal of heavy weapons was complete", Hug said.

The mission also observed the movement or presence of weapons on both sides of the contact line.

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For their part, Ukrainian politicians annulled on Thursday five crucial security agreements that allowed Russia to transport troops to a separatist region of Moldova and purchase weapons only produced in Ukraine.

The deals were effectively suspended with the onset of the pro-Russian uprising in Ukraine's industrial east 13 months ago that Ukraine blames the Kremlin for fomenting.

But the Verkhovna Rada parliament's decision means that legislative support from Ukraine's dominant nationalist and pro-European parties would be required before such cooperation could resume once the separatist conflict is resolved.

It also underscores how little an east Ukrainian truce deal reached in February has done to rebuild trust between Russia and Ukraine.

"I know of no other country that continues to be friends with a neighbour that kills your people," Mustafa Nayyem, a prominent pro-EU deputy, wrote on Facebook.

"And only recently I learned that we still have international agreements with Russia concerning military and technological cooperation."

The five annulled laws included a strategic agreement that allowed Russia to send peacekeeping forces across Ukraine to Moldova's Russian-speaking Transdniester region.

Source: Agencies