A cyber offensive against Israeli websites launched on Monday by Anonymous, an international hacking group, has inflicted marginal damage, the Israeli authorities said.

The hacking campaign, which sought to protest against Israel's strikes in Gaza and mark the anniversary of the group's first anti- Israel operation in last April, had so far resulted in "minor slowdowns" on a few dozen official sites, Israel's domestic security service said.

Operation #OpIsrael, led by pro-Palestinian groups from the West Bank, Syria, Iran, Jordan and Malaysia, was expected to mainly target the official sites of Israeli ministries and financial and academic institutions via Anonymous' trademark denial of service (DDoS) attacks, in which targets are sabotaged by flooding traffic until crash.

Earlier on Monday the Postal Service and the Education Ministry temporarily disabled their websites to avert potential damage, the Ynet news site reported, adding that some of the mostly outdated phone numbers and emails of senior Israeli officials were published online.

To head off potential damage, some Israeli government ministries have temporarily suspended international traffic to their websites since last week, including refusal of online payments. They also halted some routine maintenance of the sites, an Israeli security source said.

Last year Anonymous' mass target on Israeli sites was preceded by a media buzz, but it ended with causing marginal damage to a few hundred small sites which were defaced and some government sites that were partially paralyzed. Some personal data were also leaked.

During Israel's military operation against Gaza militants in November 2012, the hacking group launched hundreds of DDoS attacks on Israeli sites and brought down dozens.