Secretary-General Ban Ki-moon has appointed veteran U.N. envoy Jean Arnault of France to head the new U.N. political mission in Colombia that will monitor and verify a future cease-fire between the government and the country's largest rebel group.

U.N. deputy spokesman Farhan Haq announced Arnault's appointment Wednesday as the secretary-general's special representative and head of the U.N. Mission in Colombia.

Arnault has been leading U.N. preparations for deployment of the mission and has been working closely with negotiating teams for the government and the Revolutionary Armed Forces of Colombia on a sub-commission dealing with issues on ending Latin America's longest-running guerrilla conflict.

There is a March 23 deadline for peace talks to end. But Colombian President Juan Manuel Santos said Wednesday his government may miss the deadline both sides agreed to last year.

Santos explained that he would not sign a bad agreement just to wrap things up and if there isn't an acceptable peace deal, the two sides will set a new deadline.

The government and FARC have come to agreements on many key issues in recent months after three years of talks, but they still have to hammer out a plan for disarming the guerrillas.

In a surprise move, both sides asked the U.N. Security Council on Jan. 19 to establish a mission to monitor a cease-fire. Members authorized the political mission on Jan. 25 in a resolution co-sponsored by all 15 members, a rare occurrence in the often-divided council.

Before his current role as the secretary-general's delegate to the sub-commission on Colombia, Arnault served on a high-level independent panel reviewing U.N. peace operations. He previously led U.N. missions in Georgia, Afghanistan, Burundi and Guatemala.