The tunnel near Hebron uncovered about two weeks ago by the Palestinian Authority was used by Hamas as a firing range and for other weapons training, according to PA security officials.
The discovery of the tunnel is indicative of the kind of pressure the PA security forces are putting on the military wing of Hamas.
The revelation of the tunnel caught by surprise Israeli security officials, who reportedly agree with the PA's evaluation of its purpose.
In contrast to tunnels excavated through the Gaza Strip sand, a tunnel in the West Bank is rare.
Initially, neither Israel nor the PA could understand its purpose, since it seemed to lead to nowhere.
One theory, that it was to be used to hide a kidnapped soldier, was discounted.
It is now assumed that Hamas was looking for a place to carry out military training unhindered, as well as to conduct weapons trials.
The organization is having difficulty training its activists because of the massive presence of PA forces in different parts of the West Bank.
This month, for example, PA forces arrested Hamas operatives in an open area near Tul Karm.
In addition to exposing the tunnel, the Palestinians arrested a Hamas cell in Hebron whose members were involved in the suicide bombing in Dimona earlier this year, in which one woman was killed.
The PA also uncovered a lab producing relatively sophisticated explosives.
Last weekend the PA, with Israel's assent, deployed 550 police from the National Security force, who had undergone American-led training in Jordan.
J'lem: PA getting tough on Hamas
Israeli security officials concede that the PA's efforts against Hamas are the most extensive in at least a decade.
Jerusalem is reportedly impressed by the fact that the military wing of Hamas is finding it difficult to operate openly due to the double pressure of both Israel and the PA.
As part of its war on the civil infrastructure of Hamas, known as the da'wa, the PA has shut down more than 120 charity groups and confiscated large sums of money.
Israel conducts a weekly checkup of the PA's progress in dealing with terror groups, based on a number of criteria, including the struggle against the da'wa, the arrest of activists, their interrogation and trial, and capture of weapons.
However, despite apparent progress, only a relatively small number of indictments have been issued and the "revolving door" - the release of prisoners from jail after short sentences - continues to some extent.
Israel is having difficulty ascertaining Hamas' long-term policy vis-a-vis the cease-fire in the Gaza Strip.
The organization's political echelon currently seems interested in continuing the quiet.
However, some of the Hamas military wing are said to disagree with this approach and the other Palestinian factions have criticized the cease-fire, especially because Israel has not stopped its military activity in the West Bank.
Israeli security officials say that while Hamas is reining in the other groups, it is also gearing up for another round of violence by smuggling large quantities of weapons into Gaza from Sinai and planning the abduction of Israeli soldiers stationed along the border with the Strip.
Israel is also concerned about the renewal of ties last year between Hamas and Jordan, after years of severed relations, following the expulsion of Hamas' political bureau in 1999.
The Jordanian intelligence chief recently met for the fourth time with Hamas representatives, and the country released two Hamas operatives indicted for spying against it, as part of a general relaxing of the attitude toward the Muslim Brotherhood in the Hashemite Kingdom.
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