A bomb struck a predominantly Kurdish city in southeastern Turkey on Tuesday, killing seven people and wounding 17, the local governor's office said.

Authorities said the bomb in the city of Diyarbakir was made from powerful explosives and was set off by a cell phone timer. Although nobody claimed responsibility, the blast occurred in a region where Kurdish separatist rebels are known to be active.

The explosion happened around 9 p.m. and an investigation had begun, according to a statement from the provincial governor's office, which gave the casualty toll.

CountryWatch: Turkey

The deputy governor of the surrounding Diyarbakir province, Ahmet Aydin, said children were among those killed and two of the injured were in serious condition at a local hospital. Local news stations said five of the seven killed were children.

A Kurdish news agency reported that the blast took place near an elementary school. Witnesses said the blast threw body parts over a wide area and left pools of blood from the killed and injured.

Diyarbakir is Turkey's largest Kurdish-majority city, and the blast came as Kurdish rebels fighting for autonomy in the region have stepped up their attacks.

Also on Tuesday, the Turkish military announced that authorities had defused a remote-controlled bomb planted by Kurdish guerrillas on a busy bridge near the southeastern city of Hatay, and a bomb believed placed by rebels exploded as a freight train carrying coal passed in the eastern province of Bingol, damaging three rail cars.

The United States and Turkey are taking measures to counter Kurdish militants who have training camps in northern Iraq and launch frequent raids into Turkey.

Retired U.S. Air Force Gen. Joseph Ralston arrived in Ankara earlier Tuesday for talks on how to increase U.S.-Turkish cooperation in the fight against the rebels.

More than 37,000 people have been killed in fighting since rebels of the Kurdistan Workers Party, or PKK, took up arms against the Turkish state in 1984.

Both the United States and Turkey consider the group to be a terrorist organization.

Dozens of soldiers and guerrillas have been killed in a surge of violence in southeastern Turkey in recent months, leading to a Turkish government crackdown in the region, the massing of Turkish tanks and artillery along the Iraqi border and threats to attack the main guerrilla bases in northern Iraq.

Another extremist Kurdish militant group, the Kurdistan Freedom Falcons, took responsibility for a rash of bombings last month elsewhere in the country, threatening to escalate the situation.

CountryWatch: Turkey