Nigerian President Muhammadu Buhari has vowed to continue his crackdown against corrupt officials, in a tough speech ahead of his second term in power.

“My frustration is that we cannot move faster in prosecution and punishment of corrupt persons,” Buhari told state television, in an interview broadcast late Monday.

“We made some progress, we recovered a number of fixed assets and money in banks including Europe and America.”

Buhari, 76, was re-elected in February and is due to be sworn into office for his next four-year term on Wednesday.

He came to power in 2015 on a promise to tackle endemic corruption, but critics have accused him of a political witch-hunt as many of those targeted are opposition members.

Buhari said he would push on with rooting out rampant corruption in Nigeria, Africa’s biggest oil producer, saying the legal process was what had slowed progress so far.

“Even if you are using whistleblowers, you have to go to the police… to go through the rigmarole of full investigation before prosecution,” he added.

“The frustration is it’s taking too long… I need to see that those who have frustrated our economy are punished.”

His last term was held up by squabbles with lawmakers in the National Assembly, who, among other things, blocked the passing of last year’s budget for several months.

Buhari criticised those who had opposed him.

“When they go around posing that they are the government, not the executive, then that is the problem,” Buhari said.

“I told them, how do they feel to hold the country to ransom for seven months without passing a budget? I said, personally they are not hurting me, they were hurting the country. So really in terms of patriotism, I think I rated them very, very low indeed.”