ISTANBUL (REUTERS/AFP) - A car bomb killed seven police officers and wounded around two dozen people in Turkey's Diyarbakir on Thursday, security sources and officials said, a day before the prime minister is due to visit the biggest city in the largely Kurdish south-east.

A parked car laden with explosives was detonated by remote control as a minibus carrying the police officers turned a corner on a busy street, the sources said, adding that civilians were also among the wounded.

President Tayyip Erdogan, who is on a visit to Washington for a nuclear security summit, denounced the attack, saying it showed the "ugly face" of militants "as they are cornered".

"This shows terrorism's ugly face again. The determination of our security forces will, God willing, put an end" to it, Erdogan said in a speech to the Brookings Institute.

He said 27 people had also been wounded in the attack..

The south-east has been scorched by violence since a ceasefire between the outlawed Kurdistan Workers Party (PKK) and the government collapsed last July.

The government has said it has killed thousands of militants since then, while more than 350 members of the security forces have been killed in the fighting.

Round-the-clock curfews have been instituted in parts of the south-east, where the economy also been devastated by the fighting.

One of the hardest hit areas has been Diyarbakir's historic Sur district, which is encircled by Unesco-listed, Roman-era walls.

Development Minister Cevdet Yilmaz, in the area ahead of Prime Minister Ahmet Davutoglu's visit, said the government wanted to rebuild the region.

"We are here to rebuild Diyarbakir and make it beautiful, and they want to destroy it," he said in comments broadcast live. "We will not retreat in fear."

The government has announced an ambitious restoration plan for the south-east.

There was no immediate claim of responsibility for the bomb attack. A PKK offshoot has claimed two car bomb attacks this year in the capital Ankara.

The first, on Feb 17, targeted a military bus and killed 29 people, mostly soldiers. The second, just under a month later, killed 37 in a crowded transport hub.

Nato member Turkey faces multiple security threats. As part of a US-led coalition, it is fighting Islamic State in neighbouring Syria and Iraq.

In Istanbul this month a suicide bomber, who the government said was a member of Islamic State, killed three Israeli tourists and an Iranian.