The liberal premier pointed to Israeli violence against Palestinians in the occupied West Bank and said the lack of action against such "violent extremists" was "unacceptable".
"Our country must ensure that those who commit serious crimes, for example, those who commit violence in the West Bank, can be prevented from entering our country and the European Union," De Croo told the Belgian parliament.
He suggested there could be sanctions on individuals, including "a minister who calls for the use of nuclear weapons against a population that cannot do anything and that already lives today in horrible conditions".
The Israeli military launched an operation in the besieged trip that has killed more than 10,800 people.
But it is not the first time Israel, which has occupied Gaza and other Palestinian land for decades, has carried out an assault on the enclave.