Five people were injured Wednesday when a roadside bomb exploded as a bus carrying police drove by in the southern Turkish province of Adana, state media reported.

Twin bomb attacks on Monday hit the regional headquarters of Turkey's main pro-Kurdish party in two cities, injuring more than half a dozen people and escalating tensions ahead of June 7 legislative elections.

Six people were injured in the blast at the office of the People's Democratic Party (HDP) in the southern city of Adana caused by a suspect parcel, three of them seriously, a party official told AFP.

A Turkish court has issued arrest warrants for four prosecutors and one military officer in a controversial case over the interception last year of trucks that allegedly contained arms bound for neighboring Syria, reports said Thursday.

The four prosecutors had been reassigned and then suspended after they ordered the search of several trucks and buses in the southern provinces of Hatay and Adana near the Syrian border in January 2014 on suspicions of smuggling "ammunition and arms" into Syria.

Turkish police have rounded up 12 people suspected of ties to a "terrorist organization" in a string of raids across Turkey, the governor of the southern city of Adana said on Thursday.

Local media reported the suspects were affiliated with al-Qaida and the jihadist al-Nusra Front battling the regime of Bashar Assad in Syria.