The defense establishment recently relaunched its campaign with its Western partners to block Hamas' fund-raising network, Haaretz has learned. The government, meanwhile, is considering launching an awareness campaign to highlight the link between fund-raising for Palestinian causes and terror funding.

Israeli efforts have had some success in recent years, when Western governments forced certain charity organizations to reveal their records and sever ties with the Charity Coalition, the umbrella organization for groups that raise funds for Hamas abroad.

Sometimes, however, there are legal obstacles, such as a ruling by a U.S. judge in Ohio who ordered the lifting of a freeze on the assets of an Ohio-based charity called KindHearts following an investigation by the U.S. Treasury in 2006 concerning the charity's connection with Hamas.

The judge ordered the charity to be allowed to regain control of its assets, ruling that the administration did not provide enough evidence to justify the freeze. The charity was formed in 2002 after the U.S. administration closed down the Holy Land Fund for fund-raising for Hamas in the United States.

The main organizations Israeli defense officials have identified as funding Hamas have been operating since the 1980s and early 1990s in the United States, Britain, France, Germany, the Netherlands, Belgium, Denmark and Sweden. They are considered to be affiliated with the Egyptian Muslim Brotherhood movement, on which Hamas has drawn for inspiration.

These funds have raised millions of dollars every year from Muslims in those countries and have largely been funding the Islamic charity associations in the territories. The defense establishment and its representatives abroad argue that since the mid-1990s, Hamas has gradually taken over the organizations in the territories and the fund-raising associations abroad, and that some of the money goes toward arming Hamas and its military wing.

Hamas' need for reliable funding sources has greatly increased since the second intifada; the group must also compete with the Palestinian Authority under Fatah, which enjoys billions of dollars annually in donations and grants by Western and Arab governments.

The Charity Coalition was formed in 2001 to boost cash flow to Hamas by coordinating the activity of all charities affiliated with Hamas and the Muslim Brotherhood.

Late last year the United States declared the Coalition an illegal organization. In February this year the British charity registrar authority ordered the Coalition's U.K. branch, Interpal, to cut all ties with the Coalition.

The organization's management is based in Saudi Arabia and chaired by Yusuf al-Qaradawi, the Muslim Brotherhood's leading religious authority who in the past has approved suicide bombings in Israel.

The coalition has a Lebanese branch as well, which funnels funds originating in Iran. The Shin Bet security service estimates that in its eight and a half years of activity, the Coalition has transferred millions of dollars to Hamas.

In 2008, the reported sum was $25 million, but it is estimated that the actual figure is considerably higher.

The Coalition says that the money is given to civilian charities in the West Bank and Gaza, but defense officials monitoring the money trail say some of the funds are forwarded to Hamas militants. They say that even funds defined as education money are used to incite against Israel and aid relatives of militants who have committed attacks on Israelis.

These claims are based in part on interrogations of senior Hamas operatives arrested by the Israeli security forces, who said they had worked both for Hamas charities and its military wing, and that the money was used for both charitable and less legitimate purposes.