Turkey and allies lay siege to Syria's Kurdish-controlled Afrin

Turkish forces and allied Syrian rebels have surrounded the Kurdish-held enclave of Afrin in northwestern Syria, the military said on Tuesday.

The Turkish army besieged the city on Monday, bottling it in from the east and the west, according to a statement released and quoted by state media. No further details were given.

The siege of the enclave is a key step in Ankara's seven-week operation dubbed Operation Olive Branch. The military campaign, launched on January 20, sought to oust the Kurdish People's Protection Units (YPG) from the Afrin region of northern Syria.

Washington views the YPG as a key ally in the battle against the Islamic State group.

Turkey sees the Kurdish militia YPG as an extension of the outlawed Kurdistan Workers Party, PKK. The PKK group is designated as a terrorist group by Turkey, the US and EU.

Earlier in the month, Turkey warned the US that it was time to either make or break ties between the NATO allies that have strained badly over the Turkish military assault in Syria.

Continued fighting in Syria's northern provinces has spurred new waves of immigration across the border into Turkey, consisting of tens of thousands of families, according to aid organisations.

"More than 2,000 civilians have arrived in the area of Nubul," controlled by pro-regime forces, said the British-based Syrian Observatory for Human Rights on Monday.

Afrin is home to around 350,000 people. 

Reports that Turkish border forces have been shooting indiscriminately at fleeing Syrians led to HRW to issue an urgent plea to Turkey to end its use of "lethal force" against Syrian refugees, and to stop forcibly returning them back to the unsafe conditions from which they fled.

"Conditions in Syria are not safe for refugee returns," HRW's deputy Middle East director Lama Fakih said.

"With hostilities in Afrin contributing to the growing displacement crisis in the country, Turkey should allow the thousands of desperate Syrians seeking refuge to cross the border," Fakih added.

Turkey's next move remains unclear, however analysts expect the province to be held under siege for some time allowing them to leave in order to prevent a high-casualty offensive. ​