The Israeli military warned Tuesday that it would prevent the Gaza-bound boat carrying aid and Jewish activists from docking in the enclave, DPA reported.
A military spokesman in Tel Aviv said the navy would try without violence to stop the vessel from reaching its destination, but was prepared for any eventuality.
The Irene, sailing under a British flag, left Cyprus on Sunday and is en route to the Gaza Strip, which has been subject to an Israeli blockade since 2007.
On board are 10 left-wing Jewish activists, including a Holocaust survivor and a man whose daughter was killed in a Hamas suicide bombing in 1997.
Organisers say they are bringing "symbolic aid" to Palestinians in Gaza - textbooks, prosthetic limbs, toys, musical instruments and fishing nets.
Israel eased the Gaza blockade in June, several weeks after a attempt by Israeli naval commandos to prevent an aid ship from an international flotilla from reaching Gaza, turned violent.
Nine pro-Palestinian activists were killed in the interception, which an investigation by the United Nations Human Rights Council has since found to have been "clearly unlawful".