A ceasefire agreement between Ukraine and Russia has been reached on Thursday at Minsk, Belarus, according to reports.

The 13-point agreement, of which negotiations began on Wednesday, included a ceasefire to start at midnight on Saturday into Sunday local time. Reports say that leaders from France, Germany, Russia, and Ukraine, and other involved negotiators, spent 16 intense hours discussing the terms of the agreement.

The U.S., though it commended the agreement, said in a statement, “The true test of today’s accord will be in its full and unambiguous implementation, including the durable end of hostilities and the restoration of Ukrainian control over its border with Russia.”

Indeed, many are skeptical of the longevity of the agreement, as many points are still up in the air. Some terms that have been agreed to include withdrawing arms and troops from both side starting two days after the ceasefire agreement, and some sort of change in the constitution—though it hasn’t been specified exactly what kind of change.

Reports seem to implicate that Russia desires to set up autonomous republics, while Ukraine has been focusing on decentralization. There has also been no agreement to federalization of Ukraine, which would prevent it from joining groups such as NATO, according to the Associated Press.

The agreement also does not specify exactly where the truce line will stand, and the control of the border between Ukraine and Russia.

“We have no illusions,” Angela Merkel, the German chancellor. “A great, great deal of work still needs to be done. But there is a real chance to turn things around toward the better.”