Vessels carrying pro-Palestinian activists who are trying to break Israel's blockade of Gaza are due to arrive in the region on Friday — a move that sets the stage for a confrontation with Israel.

The 27 activists from countries including the U.S., Canada, and Ireland set sail from Turkey on Wednesday. They say their goal is to deliver medical aid directly to Palestinians in Gaza, in defiance of Israel's blockade.

Israeli military officials say they are prepared to intercept the two boats.

Israel imposed a naval blockade on the Hamas-ruled territory in 2007 in what says is a bid to keep weapons from reaching militants in Gaza.

On Thursday, U.S. State Department spokeswoman Victoria Nuland renewed a call for Americans to avoid participating in the flotilla, saying they could face legal consequences.

Last year, nine activists were killed after Israeli commandos stormed a Turkish-led aid flotilla headed for Gaza. The confrontation caused a deterioration in relations between Turkey and Israel.

In July, pro-Palestinian activists launched an unsuccessful attempt to reach the Palestinian territory.