The United States along with some Middle Eastern nations are stepping up efforts to target a “secret” Hamas investment portfolio government officials believe to be worth up to $1 billion.

To target the Hamas investment portfolio, a US official said Tuesday the Treasury Department is working with members of the Gulf Cooperation Council: Saudi Arabia, Qatar, Kuwait, Oman, Bahrain and the United Arab Emirates.

Following the Hamas terror attacks on Israel, US and Saudi officials convened an emergency meeting on Tuesday in Riyadh of the Terrorist Financing Targeting Center, which includes the United States and the GCC nations. The meeting was originally scheduled to take place in November.