Is it possible to use .AsParallel Extension Method in PCL?

I have a problem in a Portable Class Library class. It seems I cannot use .AsParallel() extension method although System.Linq is referenced. Here is the code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace PortableClassLibrary1
{
    public class Class1
    {
        public Class1()
        {
            var list = new List<String>();                
        }
    }
}

list hasn't AsParallel() method, it has only AsQueryable and AsEnumerable.

Target frameworks are .NET 4.5 and highr, Phone 8, Windows Store App (Win 8) and higher. Any ideas?