Outgoing US President and Nobel Peace Prize winner Barack Obama has signed into law a $ 618 billion defence budget for 2017 that allows the incoming Trump administration the authority to send shoulder-fired antiaircraft missiles to Al Qaeda-led rebel groups fighting in Syria, the US media reported.

The Al Qaeda-led attacks on September 11, 2001 killed at least 2,605 U.S. citizens, including 2,135 civilians and more than 6,000 others were wounded. Following the attack, the Bush administration announced a ‘war on terror’ with the goal of bringing the Al Qaeda to justice. “We’re going to get the b…….,” was Bush’s initial infamous reaction to the attack.

The US decision to pave the way for arming Al Qaeda-led rebels in Syria comes 15 years after 9/11. But if media reports quoting senior intelligence and Pentagon officials are to be believed, such support to anti-Assad groups continued unofficially since the beginning of the Syrian war as the US was looking for allies in the ongoing civil war.

On Tuesday, Russia described the US decision a hostile act. “Such a decision is a direct threat to the Russian air force, to other Russian military personnel, and to our embassy in Syria, which has come under fire more than once. We therefore view the step as a hostile one,” the Russian statement said.

According to experts, while continuous bombing by Russian and Syrian forces has severely damaged the Islamic State, the Al Qaeda-led rebel groups have grown in strength, now establishing themselves as the most ferocious fighting force against the Bashar Assad’s government.

The Al Qaeda – supported militant group, formerly known as Al Nusra Front, has expanded, in part, because its fighters also oppose the Islamic State on the battlefield and are rarely targeted in airstrikes by U.S.

An American soldier training a Syrian rebel

In June, Brett McGurk, President Obama’s envoy in the campaign against Islamic State, told the Senate Foreign Relations Committee that Al Nusra had become “Al Qaeda’s largest formal affiliate in history,”

The Al Nusra Front, which recently renamed itself the Front for the Conquest of Syria, has about 10,000 fighters, US intelligence officials told The Los Angeles Times last month. The Front has gained ground in Idlib province along the Turkish border.

“We’re not fighting Al Nusra,” Col. Christopher Garver, spokesman for the U.S.-led coalition in Baghdad, said in a recent teleconference with reporters. “We are fighting Daesh (Arabic acronym for Islamic State),” he said.

“The Syrian war has been a breeding ground for Al Qaeda and its version of jihadism,” Thomas Jocelyn, a senior fellow at the Foundation for Defense of Democracies, a Washington think tank told LA Times.

“Let that fact sink in,” he said. “Here you are in 2016 – fifteen years after Sept. 11, and Al Qaeda has the largest guerrilla army in its history answering directly to Zawahiri.”

The Pentagon had admitted last year, though in a round about way, that a group of US-trained Syrian fighters had handed over ammunition and equipment to Al Nusra Front, Al-Qaeda‘s affiliate. The acknowledgement had contradicted earlier denials by the US defence department.

“We learned late today that the NSF (New Syrian Forces) unit now says it did, in fact, provide six pickup trucks and a portion of their ammunition to a suspected al-Nusra Front [group],” Pentagon spokesman Captain Jeff Davis had said.

Nour al-Din al-Zinki, a former Central Intelligence Agency-backed group and one of the largest factions in Aleppo, recently announced that they were joining a broader alliance led by the Front for the Conquest of Syria. A second, smaller rebel group also joined that alliance, which is known as Jaish al-Fateh and includes another major Islamist rebel force, Ahrar al-Sham.

US trained Syrian rebels fighting approaching government forces

According experts, the Front for the Conquest of Syria presents a very different profile than Islamic State. Unlike Islamic State, which mostly consists of foreign fighters, the Front’s ranks are mostly filled with homegrown Syrian jihadis.

In July, the group sought to publicly rebrand itself in an online video by changing its name and declaring that it had cut all “external” ties to Al Qaeda. The group’s leader, Abu Mohammed Jolani, who wore army fatigues and a white turban, showed his face for the first time.

The announcement did not convince most U.S. counter-terrorism officials, who noted that Jolani did not withdraw his loyalty pledge to Al Qaeda.

Significantly, the original version of the controversial US bill, which has now become an act, had contained language that explicitly prohibited allocating funds for sending MANPADS (shoulder-fired antiaircraft missiles -Man-portable air-defense systems) to “any entity” fighting in Syria. That language has since been removed. The version of the bill the Senate passed in June made no mention of MANPADS.

It is unclear who in the House or Senate pushed for the MANPADS provision in the bill. The chairman of the Senate Armed Services Committee, Sen. John McCain (Republican from Arizona), has long called for delivery of the weapons to help the beleaguered rebels trying to stave off air attacks by the Syrian and Russian air force.

Rep. John Conyers Jr. (Democrat-Michigan.), who voted against the bill, said  he was “disappointed that the House of Representatives’ explicit prohibition on the transfer of these dangerous weapons into Syria was reversed — behind closed doors — by the conference committee.”

The Syrian civil war started as a largely unarmed uprising against Assad in March 2011, but quickly developed into a full-on civil war.

Staffan de Mistura, the UN special envoy to Syria, estimated in April that more than 400,000 Syrians had been killed since 2011. Nearly 11 million Syrians – half the country’s prewar population – have been displaced from their homes.