January 28, 2008 | By SABRINA TAVERNISE

ISTANBUL — In one of the biggest operations against Turkish ultranationalists in decades, the authorities announced on Saturday night that they had arrested 13 people who were part of a criminal group that was suspected of carrying out political killings and having shadowy ties to the Turkish state.

Among those arrested were three retired military officers, as well as Kemal Kerincsiz, the neo-nationalist lawyer who filed dozens of legal cases against Turkish intellectuals, including Orhan Pamuk, the Nobel Prize-winning novelist, the state-run Anatolian News Agency reported. The men were detained Tuesday for questioning but were not formally arrested until Saturday.

One of those officers, Veli Kucuk, a former major general, was believed to have been plotting to kill Mr. Pamuk, Turkish newspapers reported, citing documents from the investigation. Mr. Kucuk is suspected of running a secret unit within police forces that carried out bombings and killings for which other groups were widely blamed.

The arrests have riveted Turks, many of whom have long suspected underground links between political violence, such as the killings of members of ethnic and religious minority groups, and illegal groups within official state institutions like the military and the judiciary. But the connections have proved elusive, often because of insufficient evidence and suspiciously sloppy prosecutions.

“Everyone suspected something fishy was happening,” said Ilter Turan, a professor of political science at Istanbul Bilgi University. “But the evidence was imperfect.”

“Then suddenly this thing got uncovered.”

The operation began last June, when a giant stockpile of explosives and munitions was found in Istanbul. That led investigators to the group whose members were among those arrested Saturday.

The group’s members are xenophobic ultranationalists who are suspected of involvement in crimes, including the killings of three Christian missionaries in central Turkey last year and the killing of Hrant Dink, an Armenian-Turkish journalist.

In all, 28 people have been arrested since the operation began last June, according to the Anatolian News Agency.

Mr. Kucuk, for example, called and harassed Mr. Dink in the months when Mr. Dink was on trial under a law used against many intellectuals that prohibits “insulting Turkishness,” an English-language daily newspaper, Today’s Zaman, reported. Mr. Kucuk was part of a posse of ultranationalists who jeered at Mr. Dink during the trial.

The paper quoted the journalist’s brother, Orhan Dink, speaking at the murder trial late last year, as saying that his brother “took the Kucuk group very seriously,” adding, “He knew that both Kerincsiz and Kucuk were extremely serious and dangerous.”

Turkish news reports say the group is believed to be similar to a cold war-era arrangement, under which Britain and the United States were reported to have encouraged secret paramilitary organizations of hard-line anti-Communists in Europe to counter a possible Soviet invasion.

The reports draw parallels to recent history in Turkey, when the state tacitly supported paramilitary groups that were killing Kurdish leaders. Turkey began an open war with the militant fringe of its minority ethnic Kurdish population in the 1980s.

The last time Turks were given a glimpse of their state’s involvement with organized crime was in 1996, when one of the country’s most senior police commanders was found with a wanted assassin after the Mercedes sedan in which they were riding crashed in the western town of Susurluk. The man with the police commander was believed to have masterminded the jailbreak of Mehmet Ali Agca, the man who shot Pope John Paul II. Both men were killed in the crash, and a subsequent investigation went cold, but the incident remains etched in Turkish memory.

It is unclear the extent to which the current group is connected to Turkey’s old guard of staunchly secular elite, who control the military, the judiciary and a large portion of the country’s bureaucracy. The two groups do share a similar chauvinistic vision for Turkey, that of a pure Turkic-Muslim nation, unspoiled by religious or ethnic minorities.

Another one of those arrested, Sevgi Erenerol, worked as the press and information officer for the Turkish Orthodox Patriarchate, a group whose sole purpose seems to have been harassing the Greek Orthodox Church in Turkey, the religious leadership of one of Turkey’s few Christian minorities.

It is unclear whether Turkish authorities will have more success prosecuting this group than they did in the past. Turkey’s governing party, a new class of observant Muslim politicians led by Prime Minister Recep Tayyip Erdogan, is in the midst of a power struggle with the old guard, a fight that might propel Mr. Erdogan to press as hard as possible for results. “The government does have a stake in seeing this through,” Mr. Turan said.

So, it seems, does Mr. Kerincsiz, who in an interview this month summed up the situation dramatically.

“It’s a struggle for the future of Turkey,” he said.