ISTANBUL - Kurdish rebels on Monday detonated a bomb in southeast Turkey as a police armoured vehicle was passing by, killing at least four people, the state-run news agency reported.

The attack on a street in the mainly-Kurdish town of Silopi also injured 19 other people, five of them police officers, the Anadolu Agency said. Some of the injured were in serious condition.

Anadolu said the attack was carried out with an improvised explosive device hidden inside a manhole. The police vehicle was patrolling the streets a month after Turkey's security forces ended military operations in Silopi to flush out Kurdish militants linked to the outlawed Kurdistan Workers' Party, or PKK, and partially lifted a curfew imposed on the town.

The PKK has frequently targeted police and military personnel vehicles with bombs since a cease-fire between the rebels and the government collapsed last summer. Silopi and several other towns and districts in southeastern Turkey were placed under curfew as Turkey's security forces fought Kurdish militants there.

An estimated 500 Turkish security personnel have been killed in attacks or in conflict with the Kurdish rebels, according to the military, which claims to have killed 4,900 PKK militants in operations in Turkey and northern Iraq, where the group has a major bastion.

Limited access to conflict areas in the southeast has made it difficult to verify casualty figures.

Earlier on Monday, authorities partially lifted curfews in two more Kurdish areas where the operations caused extensive damage to housing. The Turkish government has promised to reconstruct all areas destroyed in the fighting.

Deputy Prime Minister Numan Kurtulmus said that 6,320 buildings have been damaged amid the fighting in five southeastern towns, affecting about 11,000 apartments. He put the estimated cost of demolishing and rebuilding the affected structures__ in the districts of Sur, Silopi, Cizre, Idil and Yuksekova__ at approximately 855 million Turkish lira ($289 million).

The curfew was relaxed at 5 a.m. Monday in the Yuksekova district and a village in Hakkari province. A nighttime curfew, however, will remain from 8 p.m. to 5 a.m., according to local officials. The curfew will be loosened further during Ramadan, the Muslim month of fasting, which this year begins in June.

Human rights groups have repeatedly raised concerns over dozens of civilian casualties caused by the military operations.

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Suzan Fraser reported from Ankara.

News from © The Associated Press, 2016