JERUSALEM — Most members of a group of foreign peace activists seized at sea by the Israeli navy remained in custody Friday, three days after their failed attempt to run Israel's blockade of the Gaza Strip, relatives and supporters said.

In the latest attempt by activists to break a crippling two-year blockade of Gaza, a group called the Free Gaza Movement sent the ship loaded with humanitarian supplies and 21 activists and crew from Cyprus.

The Israeli navy intercepted the ship Tuesday after it ignored repeated messages saying it would not be allowed to enter Gaza waters and ordering it to turn back.

Among those still being held Friday were former U.S. Representative Cynthia McKinney and Nobel Peace Prize laureate Mairead Corrigan Maguire, said Sandra Law, mother of detained British activist Alex Harrison.

Law, speaking to The Associated Press from her London home, said her daughter was being held together with other women from the group at Ramle jail, near Ben-Gurion airport. She said she spoke briefly to her daughter on Friday.

"The conditions (in the jail) aren't great, but they're certainly not as bad as they could be," Law said. "They're in good spirits. ... Alex is very upbeat."

She said the planned deportation of the activists may have been delayed by their refusal to sign legal documents in Hebrew, which they do not understand.

Israeli Foreign Ministry spokesman Yigal Palmor said that those who signed an undertaking to return home voluntarily could be released immediately and repatriated on the first available flight.

He said the law demanded that those who refused that option must be held for 72 hours before being served a compulsory deportation order.

He said if they choose not to fight that order in local courts they could be deported Saturday night or Sunday. He did not know exactly how many group members remained jailed Friday.

The Free Gaza Movement said several Bahrainis among the group were released after the intervention of that country's ruler, King Hamad bin Isa al-Khalifa.

Others on the passenger list included a Jordanian correspondent for Arab satellite TV station Al-Jazeera and his Yemeni cameraman as well as a Palestinian human rights activist. There were also activists from the United States, Britain, Ireland and Denmark.

A military statement issued on Tuesday said Israeli naval personnel boarded their small vessel without any shots being fired. It was ordered to the Israeli port of Ashdod and impounded.

The Free Gaza Movement has organized five boat trips to Gaza since August 2008, defying a blockade imposed by Israel when the militant group Hamas seized control of the territory from its Palestinian rivals in June 2007.