Nigerian police arrested several black market currency dealers on Thursday, after the government ordered the intelligence service to crack down on the dealers in efforts to strengthen its struggling local currency, the Naira.

The traders have also been ordered not to sell the dollars for more than 395 Naira, as the Central bank raises more concerns over the official and black market rates for the exchange.

“The police and state security service officials are raiding black marketers in Lagos and Abuja to compel an appreciation of the naira,” Mallam Adamu, a bureau de change operator told Reuters on Thursday.

The currency’s exchange rate is high in the black market, where it is trading at 460 naira per dollar unlike the official exchange rate of 305.5 per dollar.

Following the crackdown, the naira improved to about 400 to the dollar on the black market, from a low of 460, Bloomberg reported.

Africa’s second biggest economy has been hit by a shortage in its foreign currency reserves for several months, which further hit the country’s importation of goods.

Liquidity is thin and most investors are experiencing crisis in paying their workers and some firms have been forced into the black market to pay for their imports. Inflation has also hit the nation, reaching a decade-high of 16 percent in June.

Several firms are set to close operations in the nation in the wake of foreign exchange shortage.

The nation allowed its currency to trade freely in June, in efforts to bolster its economy, 16 months after the central bank pegged the naira between 197 and 199 against the dollar.

The fixed currency rate, introduced in February last year, led to a booming black market.

Nigeria’s economic crisis started in 2014, after a global fall in oil prices hit its biggest source of revenue, accounting for about 70 percent of the government’s income.

The oil crisis were compounded by several attacks on major oil pipelines in the Niger Delta region in May.

The attacks, mainly by the Niger Delta Avengers militants on plants owned by Chevron and Shell reduced its oil production to about 1.4 million barrels per day, the lowest in decades, Oil Price.com reported.

The West African nation slumped into recession in August, after posting a contraction in its Gross Domestic Product (GDP) in the first half of the year.