Israel has prevented the director of a Palestinian civil-society group from traveling abroad to attend a professional conference in Mexico.

Ubai Aboudi is the head of Bisan, one of six Palestinian groups that Israel last year designated a terrorist organization. Israeli officials declined to comment on the travel ban.

In an interview, Aboudi said he tried to exit the occupied West Bank last week in order to travel to the World Social Forum, an annual gathering of civil society groups that this year is taking place in Mexico. But he said he was stopped by Israeli officials at the crossing into Jordan.

“I was informed that I am banned from traveling. I asked why I am banned from traveling. They said they did not want to inform me,” he said. Aboudi, who is a U.S. citizen, said that just a month earlier, he traveled to Jordan without any problems.

The Bisan Center for Research and Development is a nonprofit that says it is committed to promoting a Palestinian society based on “freedom, justice, equality and dignity.” Aboudi has been arrested in the past by both Israel and the Palestinian Authority, which administers autonomous areas of the occupied West Bank, for his political activities.

Bisan is among six Palestinian human rights groups that Israel last year effectively outlawed after designating them terrorist organizations.

Israel says the groups have ties to the Popular Front for the Liberation of Palestine -- a small Palestinian faction with an armed wing that has carried out deadly attacks on Israelis. The PFLP is considered a terrorist group by Israel and its Western allies.

But Israel has provided little evidence backing up its claims against the six groups. The groups all continue to operate, though the Israeli crackdown has concerned international donors and caused some to cut ties.

Aboudi says he has no ties to the PFLP. The activists have said the Israeli move is an attempt to silence groups that have documented harsh treatment against Palestinians over the years.

“There is no explanation for what happened to me except that this was an attempt to silence the Palestinian voice,” Aboudi said.