In Germany, the country most affected by the crisis because of its Turkish community of 2 million, two Turkish businesses in Lower Saxony were firebombed before dawn in the latest attack linked to the hunger strike.
Ayse Idil Ekmen, aged 22, was the first woman to die in the protest by left-wing prisoners.
A Turkish human rights activist, Ali Kapilan, said more than 60 prisoners were in a critical condition. In a sign that the hunger strike may lead to unrest in Turkey, a senior policeman was shot dead in Istanbul by two attackers on Thursday night in what was believed to be a political killing.
Hans van den Broek, the EU commissioner responsible for relations with Turkey, wrote a letter to Turkey's Foreign Minister, Tansu Ciller, asking her to "do what she can so unnecessary loss of life is avoided".
A Commission spokesman said the letter was "forceful in its language, while understanding the efforts that are being made" by the Turkish government.
The hunger strikers demand the closure of Eskisehir prison, an institution in western Turkey whoich is known to inmates as "the Coffin", and an end to transfers of prisoners to remote provinces where it is difficult for lawyers and their families to visit them.
The Islamist-led government, which took office last month, has made some concessions to the prisoners. But it insists that the hunger strike is a politically inspired protest in which some inmates have been coerced into refusing food.
The hunger strike has caused Western governments and pressure groups to focus their attention once again on Turkey's human rights record, although the authorities in Ankara regard such foreign criticism as misguided or even malicious.
Turkey's human rights performance has aroused particular concern in the European Parliament, which approved an EU customs union with Turkey last year only after adding amendments which called on Turkey to demonstrate greater respect for human rights.
The Socialist group, the largest in the parliament, is threatening to block funds for Turkey unless the government in Ankara addresses the hunger strikers' grievances. Pauline Green, the Socialists' leader, said: "The Turkish government have used the institutions of the European Union to gain what they want and have given nothing of what they promised in return."
Germany's Foreign Minister, Klaus Kinkel, urged Mrs Ciller in a letter to carry out as soon as possible the improvements in prison conditions which the Turkish government announced on 9 July. Since the first hunger striker died last Sunday, several Turkish businesses have been firebombed in Germany, in what the authorities describe as a wave of attacks launched by supporters of the jailed left-wingers.
Italy's Foreign Minister, Lamberto Dini, said Turkey's relations with the EU could suffer "negative repercussions" unless the government took urgent steps to improve prison conditions.
The French government, while stressing France's good relations with Turkey, is pressing Ankara for a solution that respects human rights.
Criticism has been more muted in the United States, which regards Turkey as a crucial ally because of its size and location. Turkey's parliament is expected to vote soon on the future of Operation Provide Comfort, the US-led mission based in Turkey, which enforces a no-fly zone over northern Iraq.Reuse content