UPDATE 1045 GMT: Pro-Assad warplanes are bombing outside Jisr al-Shughour in northwest Idlib Province.

Some observers are speculating that Russia may be responding to Donald Trump’s Twitter intervention on Monday:

The Assad regime’s allies Iran and Russia have both maintained the drumbeat for an invasion of Idlib Province in northwest Syria, the last major opposition area in the country.

Iranian Foreign Minister Mohammad Javad Zarif, arriving in Damascus for talks including with Bashar al-Assad, said rebels must be “cleaned out” of the opposition area:

All of Syrian territory must be preserved and all the sects and groups should start the round of reconstruction as one collective and the displaced should return to their families.

And the remaining terrorists in the remaining parts of Idlib must be cleaned out and the region should be placed back under the control of the Syrian people.

Iranian and Syrian State media gave no details of Zarif’s discussion with Assad, printing platitudes such as “Western pressure on Tehran and Damascus will fail to deter them from fighting terrorism”; “the current level of relations between the two countries in various fields”; and “consultations and coordination, particularly in the light of the rapidly-shifting regional and international issues”.

Meanwhile, Russian Foreign Minister Sergei Lavrov repeated his declaration that the Assad regime has the right to “liquidate terrorists” and said the situation cannot be tolerated indefinitely.

Last week, Lavrov said rebels in Idlib were a “festering abscess” which had to be removed.

See Syria Daily, August 30: Russia on Idlib — “This Festering Abscess Needs to Be Liquidated”

The Iranian, Russian, and Turkish leaders will confer in Tehran on Friday.

Russia, Turkey, and Iran declared a “de-escalation zone” for Idlib, western Aleppo, and northern Hama Provinces last year. However, Moscow and Tehran have used the tactic elsewhere to support pro-Assad offensives, breaking the zones — in the name of removing “terrorists” and “extremists” — in areas such as East Ghouta near Damascus and across southern Syria.

To rationalize attacks in the northwest, Russia, Iran, and the Assad regime have been pushing out disinformation such as claims that rebels and White Helmets rescuers are preparing a “false flag” chemical attack. This would be followed by US, British, and French strikes on Assad regime positions.

In fact, it is the Assad regime and Russia who have been building up forces for an assault, with Moscow moving 10 missile-armed warships to the eastern Mediterranean off the coast of northwest Syria.

See Syria Daily, Sept 3: Assad’s Foreign Minister Pushes Lies for Idlib Assault

The greatest deterrent to an invasion has been Turkey, which twice held out against an offensive in meetings with Lavrov last month.

Ankara’s forces moved into northwest Syria alongside rebels from August 2016, pushing out the Islamic State and then taking over much of the Kurdish canton of Afrin. Turkey maintains a ring of 12 observation posts around Idlib, western Aleppo, and northern Hama.