Militants of Islamic State (IS) are said to be on the 'doorstep of Europe' after entering the strategically important town of Kobane just one mile from Syria's border with Turkey after three weeks of siege.
Backed by tanks and artillery, IS broke through Kurdish lines and are fighting off heavy street battles with the town's Kurdish defenders, just hours after they erected their black flag over a building near the strategically important town - as the Turkish military and observers watched on from the border.
The symbolic raising of the flag stirred concern that the town was about to fall, even though the Kurds have vowed to repel Islamic State fighters with their lives.
At least 14 Turkish tanks took up defensive positions on a hilltop on Turkish soil near the beseiged town, while a shell from the fighting struck a house and a grocery store inside Turkey, but no one was wounded.
Since it began its offensive in mid-September, Islamic State has barrelled through one Kurdish village after another as it closed in on its main target of Kobane. The assault has forced some 160,000 Syrians to flee and put a strain on Kurdish forces, who have struggled to hold off the extremists even with the aid of limited US-led airstrikes.
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UN secretary General Ban-Ki Moon denounced IS's "barbarous campaign" and called for "immediate action to protect the beleaguered civilian population" of the town, which is also known as Ayn al-Arab.
The UK-based Syrian Observatory for Human Rights, which monitors the civil war, said about 20 IS fighters managed to sneak into the eastern part of Kobani overnight, but were ambushed and killed by Kurdish militiamen.
"They're fighting inside the city. Hundreds of civilians have left," said Observatory director Rami Abdurrahman.
"The Islamic State controls three neighborhoods on the eastern side of Kobani. They are trying to enter the town from the southwest as well."
Across the border in the Turkish town of Mursitpinar, civilians have watched the battle unfold, capturing images of the town’s northern suburbs, the point closest to the border.
There were reportedly airstrikes taking place on Tuesday morning.
They reportedly heard an airstrike overnight but is not clear what the target was.
Syrian Kurdish forces have long been among the most effective adversaries of Islamic State, keeping the extremists out of the Kurdish enclave in northeastern Syria even as the militants routed the armed forces of both Syria and neighboring Iraq.
But in recent weeks the overstretched Kurds have struggled to counter the increasingly well-armed militants, who have been strengthened by heavy weapons looted from captured Syrian and Iraqi military bases.
As fighting raged on Monday, the country's defence minister said the NATO alliance had drawn up a strategy to defend Turkey, a NATO member, if it is attacked along its frontier with Syria.
The Nato treaty obliges all its members, including the UK and the USA, to defend other any other member if it its territory is attacked.
According to the Guardian, US airstrikes have failed to stop the advance on Kobane, with Kurdish fighters warning that ISIS forces are too numerous to be stopped by air attacks.
Over the weekend IS militants sparked international outrage by beheading British hostage Alan Henning, who became the fourth westerner to lose his life in a propaganda video for the Islamic State.
On Sunday, Deputy Prime Minister Nick Clegg detailed his opposition to extending RAF airstrikes against ISIS into Syria, arguing that the British Government should not "rush" to Parliament to seek MPs' approval for the step.
"We need to persuade the British people and Parliament as well that every time we put servicemen and women in harm's way we do so with a clear strategy in mind, and I think the combination of air strikes and ground forces needs to be properly thought through. That was obvious in Iraq, it's a little more complicated in Syria," he said.
IS Flies Black Flag Within Sight Of Turkish Border