According to reports, this so-called a Palestinian "terror tunnel" was discovered running into Israeli territory from the Gaza Strip. The tunnel was discovered last week by Israeli military near a communal farm along the fortified Gaza border.

Following the discovery, Israeli Defence Minister Moshe Yaalon accused Gaza's ruling Hamas Islamist movement of being behind construction of the 2.5-km (1.5 mile)-long tunnel.
"The discovery of the tunnel ... prevented attempts to harm Israeli civilians who live close to the border and military forces in the area." 
They have since halted the transfer of building material to the enclave.

While there has been no claim of responsibility in Gaza, a spokesman for Hamas's armed wing had Tweeted that "the determination deep in the hearts and minds of resistance fighters is more important than tunnels dug in the mud".

Reuters via Business Insider