Romania's political crisis deepened on Friday after a key government ally said an emergency decree that would dilute the government's anti-corruption fight was not constitutional.

Ombudsman Victor Ciorbea, who previously backed the government's ordinance, reversed his position on Friday and said he would tell the Constitutional Court that the decree passed overnight on Wednesday to decriminalize official misconduct was "not justified," and the measure risked "taking out of the reach of criminal law almost all the public administration".

Earlier, Justice Minister Florin Iordache said he stood by the law, defying strong criticism from home and abroad and days of massive protests.

Iordache, who had temporarily handed over his duties to a subordinate, told reporters on Friday: "I take responsibility for this ordinance." The ruling center-left Social Democratic Party has defended the decree, which has sparked some of the biggest protests in 25 years.

Romania's Constitutional Court will rule on the legality of the law on Tuesday, the last legal resort to stop it.

Speaking at a European Union summit in Malta on Friday, President Klaus Iohannis called the situation "very complicated."

"We have hundreds of thousands of my Romanians out on the streets, and I trust them. I trust my people," Iohannis said.

"I believe in Romania... European values have to prevail and this is what I believe will happen. "

Amid strong international criticism, US State Department spokesman Mark Toner said the US was "deeply concerned" about recent measures "that undermine rule of law and weaken accountability for financial and corruption-related crimes."