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Ukraine has pulled back its troops from several villages in the border region of Kharkiv due to intensified pressure from Russian forces.
A military Spokesman said, "Soldiers had come under heavy fire and moved to "more advantageous positions" in two areas of the north-eastern region."
President Volodymyr Zelensky has cancelled all upcoming foreign trips as troops struggle to contain the new cross-border incursion, with several towns and villages coming under heavy fire.
His press secretary, Sergiy Nykyforov, said the president had "instructed that all international events scheduled for the coming days be postponed and new dates coordinated".
A spokesman for the military said in a statement that the decision to move troops from the Lukyantsi and Vovchansk areas was taken to "preserve the lives of our servicemen and avoid losses".
They said the situation "remains difficult" but insisted that its forces were "not allowing the Russian occupiers to gain a foothold".
Ukraine's head of intelligence, Kyrylo Budanov, had earlier said troops had stabilised the front line.
Thousands of civilians have fled west in recent days towards Ukraine's second-largest city of Kharkiv - including from the town of Vovchansk, located 74km (45 miles) away.
Oleksiy Kharkivskiy, Vovchansk's police chief, said on social media that fighting was intense and Russian forces were establishing positions inside the town.
"The situation is extremely difficult. The enemy is taking positions on the streets of the town of Vovchansk," he said.
