Qatar has thrown its weight behind Turkey's military offensive against Kurdish militia in Syria, coming to the defence of the "national security" of one of its closest allies.

"The state of Qatar reaffirmed its support for the efforts of the republic of Turkey to maintain its national security in the wake of the breaches and terrorist attacks carried out inside Turkish territories," foreign ministry spokeswoman Lolwa Al-Khater said.

Speaking to Qatari media on Monday, Khater said Turkey's launch of Operation Olive Branch was "driven by legitimate concerns related to its national security and securing its borders, as well as protecting the territorial integrity of Syria from the danger of secession".

Qatar's announcement came as Turkey's President Recep Tayyip Erdogan vowed to step up an offensive against Kurdish targets in neighbouring Syria and Iraq.

The operation, which includes an air and ground campaign involving Ankara-backed Syrian rebels, aims to oust the People's Protection Units (YPG) from Afrin in northern Syria.

Turkey views the YPG as a terror group and an offshoot of the Kurdistan Workers' Party (PKK), which has long fought for autonomy.

The YPG denies aiming for separatism.

Turkey's offensive is complicated by the United States' relationship with the YPG, which it relied on to help oust Islamic State jihadists from their Syrian strongholds.

Qatar has grown closer to Turkey since June when Saudi Arabia, the UAE, Bahrain and Egypt cut all relations with Doha, which they accused of ties to Islamist extremists and Shiite Iran.

Ankara has since stepped in, providing food imports and political backing to Qatar amid the boycott.

The offensive on Afrin has also surfaced as a point of contention among the Gulf states.

UAE state minister for foreign affairs Anwar Gargash on Sunday warned that the operation risks further rupturing the unity of Arab states.

"The developments around Afrin reaffirm the need to rebuild and restore the concept of Arab national security," Gargash tweeted.

"Without that, the Arabs will be marginalised."

Turkey has a military base in Qatar and both countries have been unstinting in their opposition to Syrian President Bashar al-Assad.

Qatar's Emir Sheikh Tamim bin Hamad Al-Thani was the first foreign leader to phone Erdogan during Turkey's failed coup in July 2016.