KYIV – Ukraine’s army says three of its soldiers have been killed by an explosive device in eastern Ukraine, bringing to five the number of troops killed in the region this week, the latest casualties of a six-year conflict with Russia-backed separatists.

The three service personnel died on February 14 when an unknown device exploded while they were on their way to take positions near the town of Novoluhanske in the region of Donetsk, according to the army.

The office of President Volodymyr Zelenskiy, who is on an official visit to the United Arab Emirates, said he had sent the country’s defense minister and its chief of staff to eastern Ukraine to investigate the incident.

“An immediate investigation is needed so that similar tragedies do not repeat in the future. I am waiting for their report on the circumstances immediately after my return” to Ukraine on February 15, a statement quoted Zelenskiy as saying.

The deaths come three days after two government soldiers were killed in combat in the Donetsk region, despite a cease-fire that has been in place since last summer.

Fighting between Ukrainian government forces and the separatists holding parts of the Donetsk and Luhansk regions has killed more than 13,200 people since April 2014.