Islamic State militants have reportedly advanced to southern and eastern districts of Kobane, a strategically important Kurdish town along the Syria-Turkey border.

The fall of Kobane would further undermine the security of the Kurdish-majority region in northern Syria. It also raises questions over the effectiveness of the US-led bombing campaign in Syria against the self-declared Islamic State.

IS fighters fought their way into the eastern side of the city on Monday as they pushed back its Syrian Kurd defenders, the BBC reports. The militants then raised their black flag on buildings and hills.

"These neighborhoods are Kobane's shantytowns and there are still civilians there who couldn't flee," Ismet Sheikh Hasan, a senior defense official in the Syrian Kurdish region, told the Wall Street Journal.

Mustafa Bali, a spokesman for Kurds in Kobane, told Agence France-Presse that 2,000 civilians were evacuated on Monday and that all civilians were ordered to leave.

More than 180,000 refugees from around Kobane have already poured over the border into Turkey since the siege on the city started three weeks ago, the Wall Street Journal reports.

IS fighters have already captured more than 300 Kurdish villages around Kobane, but the street-to-street fighting on Monday put them within a mile of the city center. They now surround the city on three sides.

The Britain-based Syrian Observatory for Human Rights reported new airstrikes by the US-led coalition on the outskirts of town overnight. But observers on the ground said the airstrikes have done little to slow the advance of IS fighters.

An IS victory would mean more than "potential new smuggling lines for fighters and supplies," the Washington Post reports:

Kobane’s fall also would highlight the limitations of US-led airstrikes to blunt ground offensives by well-armed Islamic State units. In Iraq, the group’s fighters have gained territory against the military and allied militiamen despite facing intensified air attacks. The US military said its forces and those of partner nations conducted three strikes against Islamic State targets in Syria, including south of Kobane, on Sunday and Monday using fighter and remotely piloted aircraft. Separately, U.S. military forces used remotely piloted aircraft and helicopters to carry out three strikes in Iraq.

Turkey has so far refrained from aiding the Syrian Kurds trying to hold Kobane. Its parliament authorized military operations against IS in Iraq and Syria last week.

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The US has pushed Turkey to take a more active role in the battle against IS. Senior US officials are scheduled to hold meetings in Turkey this week in an attempt to strengthen the NATO coalition formed to take on the extremist group, the Wall Street Journal reports.

Natasha Underhill, an expert on terrorism in the Middle East at Nottingham Trent University, discussed the implications of a possible spillover into Turkey with the Guardian: