The MV Rachel Corrie, a cargo ship carrying hundreds of tons of aid and supplies, is expected to reach Israel's coastal waters by Saturday morning, though Israel's prime minister has vowed the ship will not reach land.
The Gaza-bound vessel is on an apparent collision course with the Israeli navy, creating the potential for a second clash just four days after Israeli commandos raided a six-ship flotilla, killing nine activists aboard the main vessel.
Israeli officials said they hoped to avoid a conflict with the activists on board the vessel, but Prime Minister Benjamin Netanyahu told his cabinet Thursday that the ship would not breach the blockade.
Irish Nobel Peace Prize laureate Mairead Corrigan, who was on the ship with other activists, said they were determined to press on but would offer no resistance if Israeli forces came aboard.
"We will sit down," she told The Associated Press in a telephone interview from the ship. "They will probably arrest us ... but there will be no resistance."
Eleven passengers are on board, including Corrigan and a former U.N. humanitarian coordinator in Iraq, Denis Halliday.
Israel has stood by its maritime blockade in the face of withering international pressure following the raid, urging the activists to head for the southern Israeli port of Ashdod, where the cargo would be inspected and then transferred to Gaza.
But the activists, who are carrying a cargo of hundreds of tons of aid including wheelchairs, medical supplies and concrete, have rejected the Israeli offer. Greta Berlin, a spokesman for the Free Gaza group, said the 1,200-ton ship will not stop in any port on the way.
McGuire said Friday afternoon the ship was 134 miles off the Gaza coast and was expected to reach Israel's 20-mile exclusion zone Saturday morning.
Israel imposed the blockade on Gaza three years ago after Hamas overran the territory. The militant group has repeatedly bombed civilian targets in Israel with weapons that have been smuggled into Gaza via the sea, according to Israel's Ministry of Foreign Affairs. Israel insists the blockade is necessary to keep weapons and weapons components out of Gaza.
Robert Margolis, an expert in international maritime law based out of Vancouver, Canada, said no boats, including civilian and enemy vessels, can enter a blockaded area when a maritime blockade is in effect.
"Israel is acting under the customary maritime law of blockade," Margolis told FoxNews.com. "You're allowed to do that; they declared a blockade over a port."
Margolis said Israel is acting "completely" within guidelines of blockades under international maritime law. Any vessel that violates a blockade, including the Rachel Corrie, may be captured, boarded or even attacked under international law.
"If [the Rachel Corrie] insisted on going all the way to Gaza, then the Israelis have the right to board it, not to sink it," said Margolis, citing guidelines regarding appropriate use of force. "Rather than sink it, Israeli commandoes would board the vessel."
Once a blockade is established, Margolis said they must be enforced.
"You can't have a blockade where you don't try and stop every vessel," he said. "Blockades fail from non-enforcement. The law of blockades require enforcement; there's no such thing as a paper blockade."
In Washington, the State Department said U.S. officials had been in touch with "multiple" countries, including the Israeli and Irish governments, about the latest effort.
"Everyone wants to avoid a repetition of this tragic incident," spokesman P.J. Crowley said. He added that the U.S. had been in contact numerous times with Israeli authorities in recent weeks. "We urged caution and restraint," he said.
International condemnation continued Friday, with protests in Syria, Greece, Bahrain and Malaysia, where some demonstrators burned Israeli flags and carried mock coffins. In Norway, the military canceled a seminar scheduled for later this month because an Israeli army officer was to have lectured.
Israel has allowed ships through five times, but has blocked them from entering Gaza waters since a three-week military offensive against Gaza's Hamas rulers in January 2009.
On Monday, it sent naval commandos to board a flotilla of Gaza-bound ships after failing to persuade it to dock in Israel. Activists on one ship scuffled with the commandos, who opened fire, killing eight Turks and an American of Turkish descent.
Israel claims the activists ambushed the commandos after they descended onto the board from helicopters, and the military and Turkish TV have released videotape that backs up that claim.
Returning activists admitted fighting with the Israeli commandos but insisted their actions were in self-defense because the ships were being boarded in international waters by a military force.
All of the violence took place on the lead boat, the Mavi Marmara, which was carrying hundreds of activists sponsored by an Islamic aid group from Turkey, the Foundation for Human Rights and Freedom and Humanitarian Relief. Israel outlawed the group, known by its Turkish acronym IHH, in 2008 because of alleged ties to Hamas.
Israel earlier this week deported the nearly 700 activists it rounded up from all six ships. It also offered to transfer some of the aid from the ships to Gaza, but Hamas refused entry. The Islamic militant group demanded the lifting of the blockade in full.