All 24 Ukrainians captured by Russia last year are expected to be part of an imminent prisoner swap between Kiev and Moscow, the head of their defence team told AFP on Saturday.

Ukraine's security service on Friday said it had foiled a plot to murder the war-torn country's interior minister and several members of parliament.

Interior Minister Arsen Avakov has been an outspoken critic of Russia and faces prosecution in Moscow for his tough approach to pro-Moscow fighters in the east of the ex-Soviet republic.

Ukraine's army said on Wednesday that a new nine-day truce with pro-Russian insurgents was holdings despite small skirmishes that claimed the lives of two government soldiers this week.

"A relative calm on the front is holding," Ukrainian military spokesman Andriy Lysenko told reporters.

Ukraine's security services said Thursday they had detained four members of a pro-Russian group suspected of plotting to blow up a block of flats in Kiev.

"They planned to blow up a building in Obolon and were caught red-handed," Olena Gitlyanska, spokeswoman for the SBU security services, told AFP, referring to a large residential area in northern Kiev.

Ukraine was in shock Tuesday after fierce clashes outside parliament killed three policemen and wounded 140 people as tensions flared over controversial legislation giving more autonomy to pro-Russian rebels.

It was the worst unrest in Kiev since a bloody uprising ousted a Moscow-backed president in early 2014, unleashing a separatist insurgency in the industrial east that has killed thousands of people.

Three civilians have been killed in east Ukraine as government forces claimed Saturday that shelling by pro-Russian separatists hit a record high since the start of a tattered truce in February. 

Authorities in Ukrainian-controlled territory along the frontline told Agence France Presse that shelling over the past day had killed two civilians and wounded 15 more. 

Four civilians were killed in intense shelling attacks between the Ukrainian army and pro-Russian rebels in the separatist east of the war-torn state, officials from both sides said Thursday.

"Two civilians were killed as a result of shelling in Dzerzhynsk," about 50 kilometers (30 miles) north of the rebels' de facto capital Donetsk, representative of the region's Kiev-appointed administration's health department told Agence France Presse.

Former Ukraine president Viktor Yanukovych has thanked Russian President Vladimir Putin for "saving my life" during the bloody demonstrations that led to his ouster.

Yanukovych, currently exiled in Russia, told the BBC that he would like to return to Ukraine one day and blamed the country's plight on the demonstrators who occupied Kiev's Maidan Square -- the focal point of the uprising against his rule.

U.S. Secretary of State John Kerry on Monday pressed his Russian counterpart Sergei Lavrov to ensure that Moscow respects the ceasefire in eastern Ukraine, the State Department said.

In a telephone call to Lavrov, Kerry "urged Russia to seize the opportunity of upcoming meetings of the Trilateral Contact Group and its Working Groups to accelerate progress on implementing the Minsk agreements," signed in February, said John Kirby, a State Department spokesman.

Ukraine urgently evacuated hundreds of residents Tuesday from the site of a series of fuel depot blasts near Kiev that set off a ferocious fire and left several people missing and at least one confirmed dead.

The defense ministry said it was also taking emergency measures to prevent the flames engulfing a nearby military airbase which has MiG-29 fighter jets and munitions on site.