Kiev (AFP) - Four Ukrainian soldiers and a civilian were killed in the deadliest 24-hour period in Ukraine's eastern separatist war zone since the start of an Easter truce, officials said Wednesday.

The military campaign's headquarters in Kiev said three soldiers had been near the town of Debaltseve, a transport hub connecting the Russian-backed separatist fiefdoms of Lugansk and Donetsk where intense clashes raged in early 2015.

It said one of them died after being wounded by a grenade he had thrown at advancing Lugansk fighters as he tried to avoid being taken captive.

Kiev said two other soldiers were killed in a nearby firefight.

Ukrainian military spokesman Andriy Lysenko said the fourth combat death occurred in Avdiivka, a flashpoint suburb of the rebels' de facto capital of Donetsk controlled by Kiev.

The insurgents said separately that a civilian had died from wounds she sustained Tuesday in an alleged attack by Ukrainian forces 15 kilometres (nine miles) south of Donetsk.

Ukraine has now reported losing 19 soldiers in fighting since the latest temporary truce agreement went into effect on April 1.

The separatists reported 10 combat losses last month, which was one of the most peaceful in over three years of fighting that has claimed more than 10,000 lives.

But April was also punctuated by the death in an apparent mine blast of an American paramedic who worked with the Organization for Security and Co-operation in Europe (OSCE) while on a mission in Lugansk.

The loss was the security watchdog's first in the former Soviet republic, prompting it to limit its patrols to safer paved roads and avoid dirt lanes leading to various Ukrainian and separatist positions.

The OSCE mission has been monitoring the implementation of a largely-ignored broad peace and political reconciliation agreement the warring sides signed in February 2015.

It is the only organisation that provides daily reports from the front about ceasefire violations and progress in the sides' promise to withdraw their arms.