North Sumatra ranks third after Jakarta and East Java in terms of number of corruption complaints filed in the last four years with the Corruption Eradication Commission (KPK), says the commission's deputy head.

However, of the thousands of graft cases reported by North Sumatra citizens, the KPK has only brought to court one case, involving Medan Mayor Abdillah and Deputy Mayor Ramli Lubis.

The commission's deputy head, Haryono Umar, said the KPK had received 2,290 complaints from citizens relating to corruption in North Sumatra.

The bulk of the reports came from Medan city, with 886 cases, followed by Nias regency (143), Asahan regency (140), Deli Serdang regency (135) and Simalungun regency (103).

Haryono said the number of reports received by the KPK from North Sumatra was significantly larger than most other provinces.

"Of the 2,290 complaints lodged by North Sumatra citizens with the KPK, we have studied 2,221 reports, or 96.99 percent," Haryono said during a break in a seminar in Medan on Wednesday.

"We found that only 404 reports, or 18 percent, had indications of corruption that could be followed up," he said.

Haryono said the KPK studied all 404 reports, but it had only processed 34 cases, with the remaining 370 being handed over to the police, prosecutor's office, Supreme Audit Agency, Supreme Court and the provincial supervisory board.

Haryono said almost 60 percent of all corruption cases the commission had looked into in North Sumatra involved the embezzlement of funds from the provincial budget.

He said the KPK had so far only submitted one case to the courts, involving alleged markups in the procurement of fire engines and the misuse of budgetary funds by the Medan mayor and his deputy.

He denied the KPK had been slow in handling corruption cases in North Sumatra, saying the gathering of evidence took time.

"The KPK cannot simply hand over cases to the courts without complete evidence. This is very important in order to prevent offenders from being freed from the hands of the law," he said.

KPK spokesman Johan Budi appealed to the public to continue filing reports in the drive against corruption.

He said the commission appreciated all those people in North Sumatra who had reported suspected corruption cases.