After months of battlefield stalemate in Syria, a flurry of reports from Washington, Jerusalem, Amman and the Gulf suggests a major new clandestine effort is under way to open up a "southern front" against the regime of Bashar al-Assad.

Central to the mooted plan is a renewed push to provide Syria's badly divided and often ineffectual moderate, secular rebel groups with additional funding, upgraded weapons and intelligence support.

What use they may make of such support, if indeed it fully materialises, remains to be seen.

The initiative, as reported in the region, is set against a backdrop of secret talks in the US last month between Susan Rice, Barack Obama's national security adviser, and Prince Mohammed bin Nayef, the Saudi interior minister in charge of covert action programmes in Syria.

According to the usually well informed Washington Post columnist David Ignatius, spy chiefs from Jordan, Turkey, Qatar and other regional countries also attended the discussions, focused on making a "stronger effort" to help the rebels.

This meeting has been linked in turn to last month's launching by the Free Syrian Army (FSA) of what they termed a spring offensive in the south of Syria. The offensive began days after they received new US weapons funding that may eventually total $31.4m (£18.9m), rebel commanders said.

After holding back for months owing to fears that new arms might fall into the hands of al-Qaida affiliates, unidentified American officials said Congress had given closed-door approval in January for renewed cash for light weapons intended for the moderate, secular opposition in the south.

The new US funding supposedly augments a fresh push by Gulf states to finance rebel operations in the southern region of Syria, which are ultimately aimed at Damascus. More than $1bn has been disbursed since last summer, much of it for weapons purchases in eastern Europe, according to Gulf government sources quoted by regional media.

The weapons, mostly supplied via Jordan, are said to include a variety of small arms, as well as some that are more powerful, such as anti-tank rockets. But as a result of American reservations, they do not include shoulder-launched surface-to-air missiles, known as Manpads, which could shoot down military or civilian aircraft. Saudi Arabia has stockpiles of Manpads and favours supplying them to the rebels, but the US disagrees.

According to various reports mostly based on rebel statements or official or semi-official leaks, the aim of the offensive is to push back government forces in the Daraa, Quneitra and As-Suwayda governorates in south-west Syria, so opening the road to Damascus.

The offensive has been dubbed Geneva Horan, a reference to the plains near the Jordanian border and Israeli frontier.

This new emphasis on military action along the southern front follows well documented concern that the predominance in northern and eastern Syria of jihadis belonging to the al-Nusra Front, which is linked to al-Qaida, and rival groups such as the Islamic State in Iraq and the Levant has become both destructive and counterproductive.

Detailed media reports claim the operational plans, supply routes and tactics for the new push are being overseen by a secret international operations command centre in Amman staffed by military officials from 14 countries, including the US, Britain, Israel and Arab states opposed to the Assad regime.

"Rebel fighters and opposition members say the command centre, based in an intelligence headquarters building in Amman, channels vehicles, sniper rifles, mortars, heavy machine guns, small arms and ammunition to Free Syrian Army units," the Abu Dhabi-based National newspaper reported.

Jordan denies the existence of the centre and of reportedly CIA-run rebel training facilities in northern Jordan.

"I have never heard of this," Zuhdi Janbek, director of Jordan's special branch, told the Guardian.

None of the western or Arab states that have intelligence and military staff working at the centre, the Military Operations Command (MOC), has publicly acknowledged it, but the centre's existence has become an open secret, the National claimed.

Whatever the accuracy of such reports, there is little doubt that Jordan's officially neutral stance over the Syrian war is threatened by the increasing importance of the southern front as the conflict enters its fourth year.

Despite Amman's denials, it is known to have close links with western intelligence agencies. It is also widely believed that its territory is being used by western and Arab backers of the moderate secular opposition to assist and direct anti-Assad operations.

In line with US and Saudi concerns, Jordan has stepped up arrests of jihadis transiting its territory to join hardline Islamist groups inside Syria.

Whether or not it amounts to a full-blown spring offensive, there has been increased fighting around the city of Daraa in recent weeks as the Syrian army attempts to pre-empt any rebel push towards Damascus, refugee and other sources say.

UN and EU officials in Amman say that as a result, the outflow of refugees into Jordan from southern and central Syria has doubled this month, to 1,000 or more a day. About 1.2 million Syrians are now living in Jordan, according to the Amman government.

In one reported clash last week, MOC commanders were reportedly on the brink of ordering Israeli air strikes against "strategic weapons" stored at the Tal al-Jabiyeh military complex in south-west Daraa for fear the weapons might fall into the hands of besieging al-Qaida-linked rebel groups.

According to unidentified sources, the "strategic weapons" were chemicals, possibly sarin gas. The complex was said to be less than 8km (5 miles) from Israel's border. In the event, the rebels backed off. This report could not be independently confirmed.

The apparent decision of the FSA to shift its main forces to the south coincides with a change in command. Colonel Abd al-Ilah al-Bashir, a respected battlefield leader based in the southern Quneitra governorate, replaced General Salim Idris as chief of staff last month. Idris had been blamed for failing to block the growth of jihadi influence in the north. Although President Obama says the US continues to pursue a diplomatic solution, the suggestion of increased covert US support for military action in southern Syria is plausible. There is much anger in Washington at the failure of the Geneva peace talks to make progress, in part because of Russia, Assad's most powerful ally.

These developments, if confirmed, also indicate a tentative rapprochement between the US and Saudi Arabia, the Syrian opposition's biggest regional backer, after a period when the two countries could not agree on tactics.

In a landmark visit, Obama will travel to Riyadh later this month for talks that will focus on Syria and Iran. In other recent meetings designed to coordinate policy, Obama discussed the Syrian crisis with Jordan's King Abdullah and Israel's prime minister, Binyamin Netanyahu.