He has declared a week-long unilateral ceasefire.

But with fighting still raging in eastern Ukraine, President Petro Poroshenko visited the headquarters of the military operation being coordinated against pro-Russian separatists who have refused to lay down their arms.

He has also given more details of his peace plan.

“All illegal armed groups have to understand that the ceasefire initiated by us does not mean that Ukrainian soldiers are not allowed to fight back. Any attempts by gunmen to attack will receive a strong response,” Poroshenko said in a speech on national television.

Looking ready for a fight, heavily-armed troops of the self-styled separatist Donetsk People’s Republic have taken an oath of allegiance, in apparent defiance of the Poroshenko peace plan.

In a ceremony on the town’s Lenin Square, armed fighters, some wearing masks, pledged that they would “defend the Donetsk People’s Republic to the last drop of blood”.

“We swear, we swear, we swear,” they chanted in unison.

Alexei, a miner, said he decided to take up arms last week: “I am 43. I have children. I had a job but I dropped everything to defend the homeland.”

A number of women, many in tears, rushed to hug troops and give them flowers.

“A great day, a great day, we love our army. They will protect us from fascists,” said Nastya, 32, holding hands with a masked soldier.

Russia’s President Vladimir Putin on Saturday voiced limited support for the ceasefire but insisted that talks with the rebels were needed to stop the truce from collapsing.

Poroshenko has met regional leaders and offered to respect the use of the Russian language in the east but has always refused to enter into direct dialogue with the separatists.