Palestinian fishermen ride their boats as they go fishing at the seaport of Gaza City on Oct. 10, 2016. (Xinhua photo)

GAZA, Oct. 13 (Xinhua) -- UN Special Coordinator for the Middle East Peace Process Nickolay Mladenov warned on Thursday of a new round of violent conflict between Israel and militant groups in the Gaza Strip.

He made the remarks in a news briefing in Gaza, saying that "heat in the Gaza Strip is growing up" between Israel and the Palestinian military factions, mainly Hamas movement, which rules the Gaza Strip.

He warned those "who believe that it's possible to punish the Gaza Strip and keep it under blockade."

Mladenov arrived in Gaza earlier on Thursday in a two-day visit to the coastal enclave that has been under a tight Israeli blockade for 10 years.

He also denounced those "who are digging underground tunnels and make use and invest construction raw-material in the black market for keeping the conflict flaring," saying such behavior equally endangers Palestinians and Israelis lives.

He called on an end to the rockets attacks by militants from Gaza into Israel, saying that they are always followed by "harsher and more violent" retaliations from Israel.

The senior UN diplomat assured that the ceasefire agreement, reached in 2014, is still valid, adding that "to restore calm, we need to follow up many issues, mainly reconstruction."

"We are very much concerned over the slow process of reconstruction," said Mladenov, referring to the time period after the 50-day large-scale Israeli military offensive on the Gaza Strip in 2014.

He unveiled that the UN Security Council would hold a special session next week to discuss the situation in the Gaza Strip, including bringing Israelis and Palestinians to meet over the reconstruction issue.

Israel had repeatedly banned the shipment of cements and other construction materials to the Gaza Strip, claiming that it is used by militants to build up tunnels used for carrying out attacks into Israel.