Turkish air raids hit several towns across northern Syria and Iraq late Saturday, US-backed Kurdish-led forces and a war monitor said.

The Syrian Observatory for Human Rights reported that 25 air strikes had struck areas under the control of the Kurdish-led Syrian Democratic Forces (SDF) in the countryside of Kobane and Aleppo.

What else do we know about the strikes?

The Britain-based monitor said that Syrian army positions were also targeted and the air strikes left at least 31 people dead, including both SDF and Syrian army troops.

At least 40 were injured or have gone missing, according to the war monitor. Some of those injured were in serious condition.

The Syrian Defense Ministry said "several" Syrian soldiers were killed in the northern Aleppo countryside and Hasakah province. Syrian state media had previously reported that three soldiers were killed in the strikes.

Iraqi Kurdish officials said at least 32 PKK militants had been killed in 25 air raids.

Turkey's Defense Ministry later issued a statement that its air strikes targeted bases from where militants stage attacks on Turkey. 

Turkey says strikes in response to Istanbul bombing

Saturday's attacks come just days after a deadly bombing in central Istanbul last week, which Ankara has blamed on the outlawed Kurdistan Workers' Party (PKK) . The PKK denies involvement in the blast.

"The hour of reckoning has come," the Turkish Defense Ministry said in a tweet early on Sunday.

The tweet was accompanied by a picture of a plane taking off for a night operation, but no location was specified.

Defense Minister Hulusi Akar claimed the strikes destroyed the "so-called headquarters of the terrorist organization," without giving further details.

Turkey considers the Kurdish People's Protection Units (YPG) — the main component of the SDF — an extension of the PKK.

Mazloum Abdi, the head of SDF, said on Twitter that the air strikes threatened the whole region.

"This bombing is not in favor of any party. We are making every effort to avoid a major catastrophe. If war erupts, all will be affected," he said.

SDF spokesperson Farhad Shami added in a tweet that two villages densely populated with displaced people were among the areas targeted.

He said the bombardment  had resulted in "deaths and injuries.''

"Kobane, the city that defeated ISIS, is subjected to bombardment by the aircraft of the Turkish occupation," Shami wrote.

Since 2016, Turkey has launched three major cross-border operations into Syria.

dvv, sdi/wmr, kb (AFP, AP, dpa, Lusa)