An overnight fire ravaged the Jerusalem office of B'Tselem, an Israeli human rights organisation that documents violations against Palestinians in the occupied territories, police said Monday.
Police were investigating whether the fire was caused by an arson attack, possibly by radical Jews who oppose the NGO's activities, Spokesman Micky Rosenfeld said.
The first-floor office was completely blackened inside.
Firefighters said the blaze spread quickly and that the centre of the fire was not near an electric outlet, strengthening the suspicion of arson.
The door to the organisation's office was not broken into.
One person was rescued from the fourth floor and lightly injured because of smoke inhalation.
B'Tselem Director Hagai El-Ad said there had been a rise in threats against his organization over the past weeks.
A right-wing Jewish group, Im Tirtzu, in mid-December published a video accusing B'Tselem and other "left-wing" NGOs of "treason" and its staff of working as "foreign agents" or "moles" on behalf of the Palestinians.
Right-wing government members have also been pushing for "anti-Democratic" laws seeking to "silence" such NGOs, critics say.
The fire would not stop B'Tselem from doing its work, vowed El-Ad, speaking on Israel Radio.
"Every organization like that, which comes and besmears our soldiers and us (Israelis) and supports the other side (the Palestinians), like B'Tselem, must take into account also consequences, like a couple of radicals who will want to hurt them," a neighbour in the same building, Benny Ra'anay, told reporters.