U.S. Special Representative for International Negotiations Jason Greenblatt released a statement and wrote a series of tweets blaming Hamas for “wasting resources” on terrorist infrastructure that could be used to better the lives of Gaza’s residents, and calling for the release of Israeli civilians and the bodies of Israeli Defense Forces’ soldiers being held by Hamas.

Greenblatt said in a statement: “I am deeply angered by Hamas’ continued terror activity, including the digging of tunnels that facilitate terrorist activities. Such activities show Hamas’ continued exploitation of the people of Gaza and Hamas’ threats to stability and security in the region.”

Later, Greenblatt took to Twitter to reinforce the message.

“Hamas, Palestinian Islamic Jihad and other extremists continue to build up their military strength at the expense of the civilian population, causing danger to the people of Gaza, Israel and Egypt,” Greenblatt wrote, adding that “Hamas wastes resources on tunnels & rockets to attack Israel, instead of helping the people of Gaza by getting the lights on, the water flowing & the economy growing. Hamas spews hateful rhetoric & foments a vicious cycle of violence. Gaza deserves better!”

Greenblatt also called for three Israeli civilians, as well as the remains of IDF soldiers killed near the Israel-Gaza border in August 2014, to be returned to Israel.

“I call upon Hamas to return the IDF soldiers, Hadar Goldin and Oron Shaul, who were taken by Hamas. I also call on Hamas to release the Israeli civilians they are holding—Avraham Abera Mengistu, Hisham al-Sayed and Juma Ibrahim Abu Ghanima. This is a humanitarian issue, and Hamas must return all Israelis,” stated Greenblatt.

On Monday, Greenblatt tweeted: “Hamas literally undermines Gaza’s chance for success—now building a terror tunnel under a crossing to Israel that should be a conduit toward a better economy. A terror tunnel costs roughly $5.9 million to build ($ that belongs to the people of Gaza) plus roughly $30,000 a day in lost revenue when the crossing is closed as a result. Gaza needs options besides Hamas and its enablers. Time to stop pouring money into violence and hatred, and to start investing in a real future for Palestinians in Gaza.”

Greenblatt made the tweets while in Israel for a series of meetings focused on restarting negotiations between Israelis and Palestinians.

On the trip, he visited one of the recently uncovered terror tunnels while on a tour of the Israel-Gaza border, led by IDF’s Coordinator of Government Activities in the Territories Maj. Gen. Yoav Mordechai.