German Chancellor Friedrich Merz arrived in Ukraine's capital Kiev on Sunday on an unannounced visit for talks with Ukrainian officials.
Kiev and Moscow have been attacking each other with missiles and drones, targeting key infrastructure.
"I travelled to Kiev today because Ukraine needs all our support in the coming weeks," Merz said in a statement issued after his arrival.
"If Russia is not stopped, its war machine will sooner or later turn against us."
Soon after the arrival of Merz, a bridge in Kiev was hit in a Russian attack, the city's mayor Vitali Klitschko said.
"Impact on the road surface of the Northern Bridge. Emergency services are heading to the scene," the mayor wrote on Telegram. Air raid sirens had earlier blared, warning of drones approaching the city.
Merz has been joined on the trip by Economy Minister Katherina Reiche, according to government sources.
He was met off the train by Ukraine's Foreign Minister Andriy Sybiga, who said he would hold talks with President Volodymyr Zelenskyy "on all matters of our bilateral, European, and international agenda".
"Ukraine and Germany have built a strong strategic partnership, and we are determined to deepen it further," Zelenskyy wrote on X.
Merz said in his statement that he would tell Ukraine's leader: "You can continue to count on our help."
The German chancellor earlier this week called for unity within NATO, Europe and his own country, where the far-right and Moscow-friendly Alternative for Germany (AfD) opposition is on the rise.
On Saturday, Russia warned foreigners and diplomats to leave Kiev, saying "massive" new air strikes would hit the city.
The Russian foreign ministry declared in a statement that "responsibility for any potential negative consequences rests entirely with those who ignore this warning".
Moscow had issued a similar warning in May, but leaders from countries supporting Ukraine have continued to visit despite the warnings.
Kiev mayor Vitali Klitschko said on Friday that the city, which is far from the front line of fighting between soldiers, was in a "very dramatic situation" and should now be on a war footing.
