WASHINGTON – As the North Atlantic Treaty Organization considers what action to take against ISIS, concern is mounting about the response of Turkey, a NATO member that continues to allow its borders to be crossed by Islamic fighters and launders money to finance jihad.

Informed sources tell WND that Turkey continues to keep open its borders to allow jihadists seeking to join ISIS, or Islamic State, to cross into Syria. Many of the fighters are from Europe and the United States.

Turkey has been a major gathering point for fighters throughout the world to obtain training and logistical support to join various jihadist groups and the Syrian opposition fighting Shiite-Alawite Syrian President Bashar al-Assad.

Now, many fighters from various Sunni jihadist groups have sworn allegiance to ISIS, although some openly oppose the group. The opposition, however, now appears to be waning because of ISIS' spectacular gains in recent months and its declaration of a Sunni caliphate ruled by Islamic law.

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In addition, the source, who spoke on condition of anonymity, said Turkey remains an even greater conduit of money laundering to ISIS than Qatar.

Qatar and Saudi Arabia are known financial sources to ISIS, and the funds generally are channeled through Turkey to ISIS in neighboring Syria, sources tell WND.

Analysts say Turkey is afraid of cutting off ISIS because of threats of reprisal the group has made through Turkish media.

In addition, sources say, ISIS continues to hold hostage some 49 Turkish diplomats who were captured when it took over Mosul last June. The development has been one reason for Turkey to go along with ISIS demands.

However, there appear to be more compelling reasons for Turkey to continue working with ISIS.

Turkey's backing hasn't gone unnoticed by ISIS, whose leadership now is considering rewarding Turkish businesses with contracts in ISIS-occupied Sunni areas of Iraq.

Turkey's minister of economy, Nihat Zeybekci, is receptive to the notion and has been open about encouraging Turkish businesses to invest in ISIS-occupied portions of Iraq.

”Our exports to Iraq are now down to 35 percent, but Iraq cannot easily substitute other sources,” Neybekci said. ”We think there will be a boom in demand soon. We also know that IS (ISIS) is contacting individual Turkish businessmen and telling them, 'Come back, we won't interfere.' That is not easy, of course. But when it the future Iraq is rebuilt, it will be Turkey doing it.”

WND requests for comment from the Departments of Defense and State Department on NATO-member Turkey's involvement with ISIS went unanswered. The inquiries also included a request for comment on Qatar's financial contributions to ISIS even though the U.S. has an air force base in Qatar, which also is headquarters to U.S. Central Command.

ISIS has declared creation of a caliphate extending from northeastern Syria and into western and central Iraq where all residents would be subjected to strict Islamic law, or Shariah.

ISIS also intends to extend its caliphate into the rest of the Levant, including all of Syria, Lebanon, Israel and Jordan, and has indicated a desire to take over Saudi Arabia. However a recent WND report suggests the Saudi kingdom may have paid ISIS extortion money not to attack.

Turkey's former foreign minister and now prime minister, Ahmet Davutoglu, denies Turkey is providing assistance to ISIS. Last December, Turkey placed ISIS on its own country's terrorist list.

However, Turkey to this day hasn't closed border access to Syria through which fighters and logistical equipment to ISIS in Syria flow. Critics accuse government officials of looking the other way while ISIS admits it receives help from Turkey.

In addition, Turkey continues to offer hospital assistance to ISIS fighters to recover from wounds received in fighting in Syria.

According to Middle East expert Daniel Pipes, a photo surfaced in April 2014 showing ISIS commander Abu Muhammad in a bed in Hatay State Hospital receiving treatment.

There also are claims that energy-starved Turkey has been sending close to a billion dollars to ISIS for oil shipments, predominantly from ISIS-occupied Syria and Iraq. ISIS is known to be working oil drilling installations in areas it occupies to raise revenue from illicit oil sales.

Estimates are that ISIS is exporting up to 4,000 tons of fuel to Turkey daily and is earning in return $15 million each month from energy sales. Because Turkish border guards tend to look the other way when such shipments occur, villages along the border with Syria continue their smuggling virtually in the open.

Turkish expert Hilmi Demir, who also is a professor at the Hitit University Religious Studies department, said Turkey doesn't consider ISIS as part of al-Qaida and believes the Sunni group was giving Sunnis a bad name.

Instead, Demir told Al-Monitor, ISIS similarly poses a serious threat to the Sunni population in the region. He said the Sunni label has been misused to show it is non-Shiite and instead should be regarded as Salafist-jihadists.

Demir said that making the distinction between al-Qaida and ISIS has helped ISIS to establish itself in Turkey.

”With that, Turkey also opened the door to negotiations with this group as Ankara did not consider it directly linked to al-Qaida,” Demir said.

Demir also accused the Free Syrian Army, or FNA, which uses Turkey as its base to oppose the Assad government, of joining ISIS units. The Obama administration, however, continues to receive pressure from Congress to arm the FNA to go against the militant jihadists as well as the Syrian government.