AFP journalists in Nablus reported that the entire building housing the headquarters of the Al-Tadamon Charitable Society had been sealed, with its main metal entrance gate welded shut.

"This union has been declared an illegal entity and has been shut down due to its involvement in and support for terrorism," a sign in English and Arabic posted on the front gate read.

Nablus mayor Anan al-Atira said she was taken aback by the raid.

"We were surprised after the raid to find that they had closed down a charitable organisation, the Al-Tadamon Charitable Society," Atira told AFP.

Israel's military told AFP it was looking into the details of the raid.

The charity declined to comment on the closure.

A source close to the organisation, however, told AFP that the move was linked to accusations of coordination with the Gaza-based rights organisation Al-Dameer -- allegations the source rejected.

Atira said Al-Tadamon provided services for orphans and ran at least three schools and a clinic.

She added that the charity "has been working in this country for many years, providing relief services and services for orphans".

Nablus governor Ghassan Daghlas, speaking to reporters outside the charity's headquarters, said: "To target Al-Tadamon charity is to target all the poor among our people."