ANKARA, Turkey – A Kurdish guerrilla leader jailed in Turkey, Abdullah Ocalan, should be given a retrial, the European Court of Human Rights said yesterday. The ruling outraged Turkish nationalists and could complicate the country’s efforts to join the European Union.

The Strasbourg-based court ruled that Turkey had violated international treaties by denying the head of the separatist Kurdistan Workers’ Party (PKK) a free and fair trial and access to lawyers immediately following his detention.

Retrying Mr. Ocalan or reopening his case would be “an appropriate way of redressing the violation,” the court said, but it did not set a time limit.

Turkey’s justice minister, Cemil Cicek, said: “Everybody has to trust the Turkish legal system. We have to see the decision in detail. In law even a comma is important, the details are important.”

Mr. Ocalan, who led a 15-year armed fight for Kurdish independence that claimed 30,000 lives, was captured by Turkish special forces in Kenya in February 1999. He was tried, convicted, and sentenced to death on Imrali island near Istanbul, where he remains the sole inmate of a maximum-security prison.

The sentence was commuted to life imprisonment after Turkey abolished the death penalty in 2002 in line with reforms designed to ease E.U. membership.

Mr. Ocalan took his case to the Strasbourg court, complaining that a military official had been sitting on the panel of judges during his trial.

The European Court’s rulings are binding on all 46 members of the Council of Europe and an E.U. spokesman in Brussels said the European Union expected Turkey to respect yesterday’s decision.

Western diplomats say a retrial of the man most Turks call “the baby killer” could undermine the government amid a rising tide of nationalism, much of it targeting Kurds.