This was stated by President Poroshenko during the opening of the National Security and Defense Council (NSDC) meeting on Monday, Ukrainska Pravda reports.
He stated that only after restoring full control of the border, Ukrainian authorities will impose a limited time ceasefire.
"Over 250 kilometers (of the border) have been brought back under control and checkpoints were set up," Poroshenko said.
"I can state regarding the pathways through which armed units, multiple launch rocket systems ("Grad"), artillery passed into the Ukrainian territory which they recently crossed freely - two of the most dangerous stretches of this road were closed today," he added.
According to the President, the government hopes to finally regain control of the border as early as by the end of this week.
"This is the only deterrent for implementing the ceasefire. Once the border is under control, we will introduce it," Poroshenko said.
The NSDC meeting began with a moment of silence for those killed in action.