The Turkish military says it has surrounded the Kurdish-held city of Afrin in northern Syria, the focus of an offensive against a Kurdish militia. A statement said troops and allied Syrian rebels had also captured "critically important areas". A Kurdish source confirmed that all roads into the city were now being targeted by Turkish shellfire. Hundreds of civilians reportedly fled the city to nearby areas controlled by the Syrian government on Monday. The Turkish operation aimed at driving the Kurdish People's Protection Units (YPG) militia out of Afrin began on 20 January. The Turkish government says the YPG is an extension of the banned Kurdistan Workers' Party (PKK), which has fought for Kurdish autonomy in south-eastern Turkey for three decades, and considers it a terrorist group. The YPG denies any direct organisational links to the PKK - an assertion backed by the US, which has provided the militia and allied Arab fighters with weapons and air support to help them battle the jihadist group Islamic State (IS). The Syrian Observatory for Human Rights, a UK-based monitoring group, confirmed that Turkish-led forces were besieging Afrin, 90 villages and a nearby town on Tuesday. The only road out was in range of Turkish artillery fire and was therefore impassable, it said. YPG spokesman Nouri Mahmoud acknowledged that all roads in the area were being targeted by Turkish bombardment. But he told Reuters news agency that Afrin had long been surrounded "from all directions", and that Turkey was spreading false news to boost morale. Turkey's military says 3,393 "terrorists" have been "neutralised" - a term it says means they have surrendered, been captured or been killed - since the Afrin offensive began. The Kurdish Red Crescent says more than 230 civilians, including 35 children, have also been killed and 688 civilians wounded. However, the Turkish military denies targeting civilians or civilian infrastructure, and insists that it has ensured the basic needs of civilians continue to be met. Turkey has also threatened to start an operation to clear YPG fighters deployed in Manbij, a town east of Afrin, as part of the US-backed Syrian Democratic Forces. On Tuesday, Turkish Foreign Minister Mevlut Cavusoglu said an agreement had been reached with the US on a plan for the YPG to withdraw from Manbij and for Turkish and US soldiers to be stationed there to ensure its security. The fighting in northern Syria came as a group of sick and injured civilians were evacuated from the rebel-held Eastern Ghouta outside Damascus, which is under siege by government forces. State TV showed people in wheelchairs and on crutches arriving at the al-Wafideen checkpoint on Tuesday, a day after the rebel group Jaysh al-Islam said it had agreed with the government's ally Russia to begin medical evacuations. Jaysh al-Islam later stressed it was not negotiating to leave the Eastern Ghouta and would continue to fight, even though the government has recaptured 60% of the enclave since mid-February and more than 1,100 civilians have been killed.