Violence in northwest Syria has displaced more than 30,000 people this month alone, the United Nations said Monday, warning that a looming assault could create the century's "worst humanitarian catastrophe".
Idlib province and adjacent rural areas form the largest piece of territory still held by Syria's beleaguered rebels, worn down by a succession of government victories in recent months.

President Bashar Assad has now set his sights on Idlib, and his forces have stepped up bombardment of the densely populated province since the beginning of the month.
That has prompted an estimated 30,452 people to be displaced within Idlib and parts of adjacent Hama province between September 1 and 9, the UN's humanitarian coordination agency (OCHA) said Monday.

"We're deeply concerned about this recent escalation of violence, which has resulted in the displacement of over 30,000 in the area. That's something we're monitoring very closely," OCHA spokesman David Swanson told AFP.
"There needs to be ways of dealing with this problem that don't turn the next few months in Idlib into the worst humanitarian catastrophe with the biggest loss of life in the 21st century," Mark Lowcock told reporters in Geneva.
He acknowledged that there were many rebels and fighters from "terrorist" groups in the province, but stressed that "there are 100 civilians, most of them women and children, for every fighter in Idlib".
Idlib is mostly controlled by Hayat Tahrir Sham (HTS) - an alliance spearheaded by powerful militants once linked to Qaeda.
Its population ballooned as the regime chalked up a series of victories across the country, reaching deals that saw tens of thousands of rebels and civilians bussed into Idlib.
The escalating bombardment has already damaged civilian infrastructure.
At least two hospitals and two centers running rescue operations for wounded people were put out of service by shelling and air strikes, according to the Britain-based Observatory and the Union of Medical Care and Relief Organisations, which backs medical centres in Syria.
Many made a dash for Syria's northern border with Turkey, with just under half seeking refuge in displacement camps and others living with local families or renting apartments.
Turkey, which currently hosts some 3.5 million refugees, has also said that it could not accommodate any more.
The UN has said as many as 800,000 people could be displaced by a regime assault on Idlib and surrounding areas.
Some three million people live in the zone now, about half of them already displaced by the brutal seven-year war and others heavily dependent on humanitarian aid to survive
For weeks, regime troops backed by Russia and Iran have massed around Idlib's periphery, with deadly air strikes, shelling, and barrel bombs particularly building up in recent days.
Security risks for Turkey, Europe and beyond

A Syrian government offensive in the country's northern region of Idlib would cause humanitarian and security risks for Turkey, Europe and beyond, Turkish President Tayyip Erdogan said on Tuesday in an article in the Wall Street Journal.
Erdogan failed to secure a pledge for a ceasefire from Russia and Iran, Syrian President Bashar Assad's main backers, at a trilateral summit in Tehran.
In the newspaper article, Erdogan called on the international community to take action, and warned "the entire world stands to pay the price" otherwise.
"All members of the international community must understand their responsibilities as the assault on Idlib looms. The consequences of inaction are immense," Erdogan said.
"A regime assault would also create serious humanitarian and security risks for Turkey, the rest of Europe and beyond." Idlib is the insurgents' only remaining major stronghold and a government offensive could be the war's last decisive battle.
Tehran and Moscow have helped Assad turn the course of the war against an array of opponents ranging from Western-backed rebels to Islamist militants. Turkey is a leading opposition supporter, which has troops in the country and has erected 12 observation posts around Idlib.
At the summit in Tehran, Erdogan had called for a truce, but Putin said this would be pointless, as it would not involve the Islamist militant groups that Russia deems terrorists, and Rouhani said Syria must regain control over all its territory.
On Tuesday, Erdogan said Russia and Iran were also responsible for stopping a humanitarian disaster in Idlib, and said the international community had to "throw its weight behind a political solution."
Chemical Weapons

In recent days, U.S. officials have said that they have evidence that Syrian government forces are preparing chemical weapons ahead of a planned assault on Idlib.
On Monday, U.S. President Donald Trump's national security adviser said the United States, Britain and France had agreed that another use of chemical weapons by the Syrian government would result in a "much stronger response" compared to previous air strikes.
Erdogan said that a focus on the potential use of chemical weapons alone was not enough.
"It is crucial for the U.S., which has concentrated on chemical attacks, to reject its arbitrary hierarchy of death. Conventional weapons are responsible for far more deaths," he said.
Both Turkey and the United Nations have previously warned of a massacre and humanitarian catastrophe involving tens of thousands of civilians in the event of a full-scale offensive.
Turkey, which currently hosts some 3.5 million refugees, has also said that it could not accommodate any more migrants if an attack on Idlib caused a new surge of refugees towards its border.
Germany possible military role in Syria

The German government said on Monday it was in talks with its allies about a possible military deployment in Syria.
Overseas military action remains a sensitive and deeply unpopular topic in Germany, given its Nazi past.
Government spokesman Steffen Seibert said Germany had discussed with the United States and European allies its possible military involvement if Assad's forces used chemical weapons against the last major rebel stronghold in Idlib, now under heavy Syrian and Russian bombardment.
Earlier, Bild newspaper had reported that Germany's conservative-led defence ministry was examining possible options for joining U.S., British and French forces in any future military action if Damascus again used chemical weapons.
Sources familiar with the issue, confirming the Bild report, said German and U.S. officials last month had discussed the possibility of German fighter jets helping with battle damage assessments or dropping bombs for the first time since the war in ex-Yugoslavia in the 1990s.
In a joint statement on Monday, the German foreign and defence ministries urged restraint in Syria.
"The goal is that the conflict parties ... avoid escalating an already terrible situation ... That is particularly true for the use of banned chemical weapons which the Assad government has already used in the past," it said.