EU foreign policy chief Josep Borrell said Saturday that a plan by Israel to evacuate more than one million people out of northern Gaza in a single day was "utterly impossible to implement".
Israel warned residents in the area to evacuate before an expected ground offensive against Hamas in retaliation for the deadliest attack in Israel's history.
"I am saying that, representing the official position of the European Union... (the evacuation plan) is utterly, utterly impossible to implement," Borrell told a press conference in Beijing on the final day of a three-day diplomatic visit to China.
"To imagine that you could move one million people in 24 hours in a situation like Gaza can only be a humanitarian crisis," he added, AFP reported.
EU chief Ursula von der Leyen had expressed support to Israeli Prime Minister Benjamin Netanyahu on Friday during a visit to the country.
"Europe stands with Israel," said von der Leyen, adding that the country had "a duty to defend its citizens".
But Borrell's comments in Beijing showed the limits of that affirmation, saying that Israel was also obligated to follow international humanitarian law in the process of defending itself.
"The position is clear," said Borrell. "We certainly defend the right of Israel to defend itself."
"But, as any right, it has a limit. And this limit is international law."
China's reaction to the conflict, which did not include a direct condemnation of the Hamas attacks, had been criticized by Western leaders as too weak.
Following a series of high-level talks with Chinese leaders, Borrell said that the EU and China agree on the two-state solution.
"We certainly agree that the only long-term solution to these crises that come one after the other... is to work on the solution of two states," said Borrell.
"We agreed the international community should do the utmost to prevent the further degradation of the situation that could spill over the region."