Turkey's Prime Minister Recep Tayyip Erdogan rushed to the overwhelmingly Kurdish southeast and urged calm after weeks of rioting, vowing that his government would investigate charges that security forces, and not Kurdish guerrillas, were behind a recent fatal bombing. Allegations that undercover police carried out the bombing have raised accusations of state-backed summary executions and sparked street clashes in the southeast and then in Kurdish neighborhoods of Istanbul - violence in which four have died. For decades, southeastern Turkey has been treated as a backwater province, and the appearance of a Turkish prime minister was likely to help calm tensions. The bombing has raised the uncomfortable specter of security forces carrying out summary executions, a common practice in the early 1990s, when Kurdish rebels controlled large swathes of the southeast. Those allegations are especially difficult now. The European Union agreed to start entry talks with Turkey last month and has been extremely critical of the country's human rights record.