The threats have come via emails, phone calls, and once with flowers delivered directly to the front door.

Amid months of sustained intimidation, harassment and threats, Palestinian human rights defenders are coming forward to denounce a campaign that they say aims to “plant fear” into their efforts to hold Israel accountable for human rights violationsRights-groups-say-Israel-behind-death-threats-campaign.

“This is a very organised and advanced campaign,” said Shawan Jabarin, director of Al Haq, a prominent Ramallah-based Palestinian human rights organisation.

“The goal is to stop us [from] dealing actively with the [International Criminal Court], cooperating actively with the ICC,” Jabarin told Al Jazeera. “They want to plant fear on our side … when it comes to accountability [and] when it comes to our advocacy work.”

Earlier this month, Al Haq’s researcher at the ICC, Nada Kiswanson, told the Dutch press that she had received death threats and other intimidations for several months, including letters, emails and phone calls to her home and family members. A man phoned Kiswanson’s family members in Sweden and, in heavily accented Arabic, told them she would “disappear” if her work at the ICC continued, Jabarin said.

Kiswanson also received a call from a woman purporting to be from the Dutch Health Ministry, who asked for her home address to send her a survey and information about the Zika virus. Shortly thereafter, Kiswanson received flowers at her door, a threatening note attached to them. Jabarin said the delivery originated in Amsterdam.

Previous death threats levied against Al Haq staff members have been “directly connected” to their work at the ICC, according to Amnesty International. At the same time, leaflets misrepresenting Al Haq’s work – which featured the organisation’s name and logo and asked for donations in support of refugees – were also distributed to homes in The Hague, Jabarin said

In addition, Al Haq’s international donors have received calls alleging that the organisation was being investigated for corruption, while faked internal emails told staff members that the organisation was having funding problems and that they should find new jobs, he said.

Dutch authorities have been investigating the Kiswanson case, but Al Haq did not have any information about potential suspects for that or any of the other incidents.

“Israel is behind it,” Jabarin alleged. “Criminals, all the time, they are afraid. When you start searching and looking to identify them, they will become afraid. For them, it’s easy to defeat politicians, but it’s not easy for them to defeat the human rights defenders.”

A spokesperson for the Israeli prime minister’s office did not respond to Al Jazeera’s request for comment on the allegations. Emmanuel Nahshon, a spokesperson for the Israeli Ministry of Foreign Affairs, said in a curt email: “We do not react to such preposterous allegations.”

Al Haq is not the only Palestinian rights group to receive threats recently.