ISTANBUL — Ali Babacan, a former lieutenant in Turkey’s ruling Justice and Development Party (AKP), said he planned to form a new political party by the end of the year to lead Turkey out of the “dark tunnel” it has entered as rights, freedoms and the rule of law have eroded under 17 years of one party’s rule.

Babacan, a former economy, foreign and deputy prime minister, quit the party he helped found this summer and now wants to form a new one to rebuild Turkish credibility on the international stage and draw foreign investment. He cited a weakening of institutions and a lack of transparency among the problems wrought by the AKP in recent years in a rare, expansive interview with HaberTurk late on Tuesday.

“We see that the country has entered a dark tunnel,” Babacan said. “We were compelled to start a new project after we saw that it was impossible to solve Turkey’s growing problems with the current administration.”

President Recep Tayyip Erdogan is facing a rebellion from within his own political movement after the AKP’s electoral setback earlier this year, when it lost a string of mayorships, including the biggest city of Istanbul and the capital Ankara, amid a painful economic slowdown. His erstwhile allies have accused Erdogan of economic mismanagement and undermining democracy by concentrating power in his own hands.