ISTANBUL (Reuters) - At least 20 people were killed and more than 250 wounded on Saturday when car bombers shattered two Istanbul synagogues as worshippers celebrated the Sabbath.

Turkish officials said al Qaeda might have had a hand in it.

"It is clear that this is a terrorist event with international links," Foreign Minister Abdullah Gul said as emergency services struggled to treat those caught up in the blasts, which wrecked cars and buildings over wide areas.

Interior Minister Abdulkadir Aksu said he could not rule out a role by Osama bin Laden's al Qaeda, blamed for attacks on other Jewish targets around the world in the past 18 months.

"It was like a battlefield," said Yavuz Guler, who dashed to one of the synagogues from the nearby restaurant where he works.

"The injured were in an awful state, moaning, but unable to speak. Some were screaming, there was a lot of blood and body parts on the street," the 24-year-old said.

The attackers could have been suicide bombers or may have detonated devices in the vehicles by remote control, Aksu said.

"In both cases, vans were driven by the attackers toward their targets. We believe they contained the same kind of explosives, they are the same kind of terror attacks," he said.

Istanbul health authorities said 20 people had been killed and 257 wounded in the two attacks, which hit the central Neve Shalom synagogue and another, Beit Israel, in the Sisli district around 9:30 a.m. (0730 GMT). The Neve Shalom -- "Oasis of Peace" -- was especially busy for a bar-mitzvah coming of age ceremony.

But many of the casualties were not Jews but people passing by on the busy streets outside the heavily protected synagogues.

Police officers earlier said as many as 24 had died. The Anatolian news agency said one policeman was among the dead.

RESPONSIBILITY CLAIM

A radical Turkish Islamist group, widely believed to be backed by Iran, claimed responsibility, but Aksu said he doubted a local group could mount such a large-scale operation.

"It is difficult for any Turkey-based organization to carry out an attack of this magnitude," he said at the scene.

Injured people covered in blood were carried on stretchers from around the Neve Shalom synagogue, target of a 1986 attack by Palestinians which killed 22 people. Six years later it was hit again, this time by a Turkish group. A passer-by was hurt.

Predominantly Muslim Turkey is a key NATO ally of the United States and recently offered to send troops to help secure neighboring Iraq, though it later abandoned the plan due to strong opposition from Iraq's U.S.-appointed Governing Council.

Turkey, which has a long history of homegrown political violence, also has warm relations with Israel. The Jewish state swiftly condemned the "criminal terror attacks" in Istanbul.

A senior Israeli security source told Reuters the blasts seemed to be the work of an al Qaeda affiliate, possibly seeking to target both arch-foe Israel and moderate Muslim Turkey.

Turkish Islamist group IBDA/C -- the Islamic Great Eastern Raiders/Front -- claimed responsibility in a call to Turkey's semi-official Anatolian news agency.

Jewish sites have been targeted in recent attacks blamed on militants linked to al Qaeda -- notably in Casablanca in May, a Tunisian synagogue bombed in April 2002 and Israeli tourists in the Kenyan seaside city of Mombasa last November.

Turkish President Ahmet Necdet Sezer issued a statement condemning the bomb blasts as did numerous world governments.

JEWS IN TURKEY FOR 500 YEARS

Istanbul, as the capital of the Ottoman empire, has a long history of Jewish presence, notably bolstered after Spain expelled Jews in 1492. About 30,000 live there now, some of whom still speak a medieval form of Spanish known as Ladino.

"If they are trying to scare the Jewish community here, they will fail. We have been here for 500 years and we will stay. Terror will not win," Roberto Abudara, who had been in the Sisli synagogue when the attackers struck, told Reuters.

Edi Baruh, a 30-year-old Turkish Jew said his father-in-law, who was at the Neve Shalom synagogue when the bomb exploded, had told him up to 300 people were there, 10 times more than usual, because it was a bar-mitzvah, a coming of age for a boy.

Gul said the attacks would not affect government policy.

"We will continue our struggle with strong determination against terror," he said.

Roland Jacquard, head of the International Terrorism Observatory in Paris, said the likeliest suspect was the militant group Ansar al-Islam, which the Pentagon has called the principal "terrorist adversary" of U.S. forces in Iraq.

Jacquard said claims of responsibility should be treated cautiously, but that IBDA/C was very close to Ansar, long based in Iraq's Kurdish areas traditionally hostile to Turkey.

Mustafa Alani of the Royal United Services Institute in London said any connection with al Qaeda was more likely to be ideological than organizational.

"There is no history of al Qaeda operating in Turkey. It's very hard to say al Qaeda is involved in this attack. I think the activities of al Qaeda now are concentrated on two states -- Saudi Arabia and Iraq," he said by telephone.