Romania's liberal government, installed in November of last year, said it had encountered "unexpected" expenses.
It may now run the risk of disciplinary action from Brussels.
At a press conference, Citu indicated that the previous left-wing government's spending plans had been to blame for the deficit increase.
"Last year funds allocated to investment ended up being directed towards salaries and welfare payments," Citu said.
The previous leftist government had projected a deficit of 2.76 percent for 2019, which experts described as unrealistic even at the time.
The new liberal government was initially expecting the figure to reach 4.4 percent.
Spending on public sector salaries was up 19 percent compared with 2018 whereas public revenue only increased 10.7 percent.
Citu said the government should be able to bring the deficit down to 3.6 percent over 2020.
"It's not just a promise of mine that I want to keep, but if we don't respect this (3.6 percent) target we will lose what I see as the most important thing right now, and that is investors' trust," Citu said in a TV interview on Monday evening.
He predicted "a hard fight" ahead to keep to this threshold given upcoming local and national elections this year.
The International Monetary Fund (IMF) and credit rating agencies have urged the government to abandon a 40 percent hike in pensions voted through by the previous government and due to take effect in September.
According to the independent Fiscal Council watchdog, the pension hike could mean the deficit going beyond 4.6 percent in 2020.