Israeli police deployed reinforcements around Muslim and Christian sites in Jaffa on Sunday after graves in the mixed port town were found to be desecrated, a police spokeswoman said.
"Police reinforcements have been deployed around the Muslim and Christian religious sites which are considered to be sensitive," spokeswoman Luba Samri said, adding that police had been in touch with Muslim and Christian officials in the Mediterranean town which lies immediately south of Tel Aviv.
"The police have been ordered to prevent any provocations," she said.
Jaffa residents on Saturday discovered that 26 graves had been daubed with anti-Arab graffiti reading "Death to Arabs" and "price tag" -- 22 of them in a Muslim cemetery and four in a nearby Christian burial site.
Several hours later, a Molotov cocktail was thrown at a local synagogue in an apparent revenge attack which did not cause any damage.
Israeli Prime Minister Benjamin Netanyahu denounced the attacks in remarks at the start of the weekly cabinet meeting.
"We are not prepared to tolerate any vandalism, especially that directed against religious sensitivities. The State of Israel is both a tolerant state and a very intolerant state," he said in remarks communicated by his office.
"Our tolerance is toward religious sensitivities... Our intolerance is directed toward those who oppose these practices and this way of life," he said. "We will act against them to the fullest extent of the law."
Although the damage was discovered on Saturday, it appeared to have been carried out "a week or so ago," Samri said, explaining they were old cemeteries which were not regularly visited.
Arab officials in Jaffa denounced the attacks as another incident of "racist aggression," and urged people not to "react to the provocation."
"We fear there could be more dangerous events like what happened," said Sheikh Ahmad Ajweh, head of the Islamic Movement in Jaffa.
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"It is the natural result of the current Israeli government's policy -- which is led by the extreme right -- of incitement and abuse, and of enacting racist laws against Arabs and Muslims," he told AFP.
More graffiti was uncovered on Monday in Bat Yam, just south of Jaffa, where the words: "Death to Arabs" and "Rabbi (Meir) Kahane was right" daubed on the walls of two residential building, referring to a far-right activist who routinely called for Arabs to be expelled from Israel.
They also wrote: "Maccabi Haifa does not want Arabs on the team" fuelling suspicions that football hooligans could be behind the latest attacks. Police said it was not clear if the two incidents were linked.
"Price tag" is a term which tends to refer to acts of vengeance by extremist Jews against Palestinians or Arabs, which usually occur in the West Bank, although there have been incidents of its use inside Israel.
The vandalism was discovered just five days after an arson attack on a mosque in the northern Bedouin town of Tuba Zangaria in which the perpetrators scrawled the words "tag" and "revenge" on the walls of the building.
Samri said the increased police presence, "particularly around Muslim holy sites", had been ordered by police chief Yohanan Danino following Monday's pre-dawn attack in Tuba Zangaria near the Sea of Galilee.
Police have arrested one suspect although details of his identity are subject to a gag order. His remand in custody has been extended until October 11.
Reports in the Israeli press said he was an 18-year-old Jew from the Galilee region, who was arrested in the northern West Bank where he attends a Jewish seminary in the hardline settlement of Yitzhar.
He had reportedly been barred by the authorities from returning to the settlement on suspicion he was planning to attack Palestinians.
Ron Huldai, who is mayor of Tel Aviv-Jaffa, said he was "ashamed" by the authorities' inability to halt such attacks.
"The price tag phenomenon has been going on for years. The police and the Shin Bet have hardly arrested anyone," he said, referring to Israel's internal security services, which are responsible for investigating Jewish extremism.
"As a Jew living in this country, I am ashamed."
Samri said the police had recently set up a special unit to look into Jewish extremism.