Greenblatt to Erekat: 'Get serious' and 'use your intellect'US envoy, PLO officials extend twitter spat to 6th day.U.S. Envoy for Middle East negotiations Jason Greenblatt on a visit in Israel(photo credit: AMIR COHEN/REUTERS)
U.S. Envoy for Middle East negotiations Jason Greenblatt on a visit in Israel(photo credit: AMIR COHEN/REUTERS)Updated: