America steps up efforts to cut off ISIL funds

Over the past month, U.S.-led air strikes have hit at least 175 targets in the main oil-producing region held by Islamic State in Iraq and the Levant (ISIL), as Washington intensifies efforts to disrupt a key revenue source estimated to provide more than $1 million a day to the group.

Those strikes include 116 oil tanker trucks hit by coalition forces earlier this week. The United States targeted the vehicles for the first time in the wake of last Friday's suicide and shooting attacks in Paris, for which ISIL has claimed responsibility.

The stepped-up bombing campaign has also targeted oil rigs, pumps and storage tanks, according to a Reuters tally of air strikes provided by the Pentagon since Oct 22.

Navy Capt. Jeff Davis, a Pentagon spokesman, said that in an effort to warn the truck drivers to leave the area in advance of Sunday's attacks, leaflets were dropped and coalition planes conducted low-level "show of force" flights over the site.

Davis said the coalition had determined that more needed to be done to inhibit ISIL's generation of oil revenues in Syria and Iraq. The Treasury Department said last year that the group earned nearly $1 million a day from illicit oil sales; the Pentagon believes that sum has risen to nearly $1.4 million a day.

A 2014 report from the Soufan Group, a global research group, identified oil production and "extortion/taxation" of locals in occupied regions as ISIL's two primary sources of revenue.

Since the earliest days of the U.S.-led bombing campaign, some parts of ISIL's oil infrastructure have been attacked, but the effort is now intensifying. Although Sunday's strikes came just two days after the Paris attacks, Pentagon officials said there was no direct connection between the two events.

Other U.S. government agencies have redoubled their investigations into ISIL funding in the aftermath of the attacks.

Authorities in the U.S. Treasury Department, scrambling to respond to the attacks, delayed scheduled computer maintenance so they could check a key database used by financial institutions to report suspicious transactions that could be linked to terrorism.

The U.S. Treasury Department's Financial Crimes Enforcement Network (FinCEN) circulated an email on Friday evening announcing that computer maintenance was being postponed due to the Paris attacks.

FinCEN Director Jennifer Shasky Calvery declined to say whether law enforcement officials had uncovered any transactions linked to suspects identified in the Paris attacks.

However, she said the Bank Secrecy Act database has been useful in understanding ISIL and "foreign terrorist fighters." She said queries of the data are producing roughly 1,000 alerts each month on possible activity linked to ISIL, up from 800 in April.

"I can tell you that the information being filed by our financial institutions is very helpful," Shasky Calvery said.

Al Jazeera and wire services