NATO has condemned Russian incursions into Turkish airspace as an "extreme danger" and demanded that Moscow halt all attacks against the Syrian opposition and civilians.
The alliance summoned the ambassadors of its 28 member states on Monday for an emergency meeting to respond to what Secretary-General Jens Stoltenberg called "unacceptable violations of Turkish airspace".
"[We] strongly protest these violations of Turkish sovereign airspace and condemn these incursions into and violations of NATO airspace. [We] also note the extreme danger of such irresponsible behaviour," NATO said after the emergency meeting.
US Secretary of State John Kerry said his country was "greatly concerned" about the incursion over the weekend.
"We are greatly concerned about it because it is precisely the kind of thing that, had Turkey responded ... it could have resulted in a shootdown, and it is precisely the kind of thing we warned against," Kerry said during a visit to Chile.
Earlier, Turkey's prime minister said Russia had described its warplane's violation of Turkey's airspace as a "mistake" while describing the country's entry into the conflict in Syria as an escalation.
Ahmet Davutoglu, speaking in a live interview on HaberTurk TV on Monday, said that Turkey's rules of engagement were clear, whomever violates its airspace.
A Russian aircraft entered Turkish airspace near the Syrian border on Saturday, prompting Turkey to scramble two F-16 jets to intercept it and summon Russia's ambassador in protest.
"The Turkish armed forces are clearly instructed. Even if it is a flying bird, it will be intercepted," Davutoglu said.
He warned Turkey's enemies and allies not to infringe its airspace, but he dismissed the notion of tensions with Russia.
"The Syrian issue is not a Turkey-Russia crisis," he said.
"Our channels with Russia remain open," he said, hoping that Moscow would give up on "wrong attitudes".
Feridun Sinirlioglu, Turkey's foreign minister, contacted his Russian counterpart, Sergey Lavrov, warning him not to repeat similar incidents.
Turkey and Russia remain on opposing sides of the conflict, the latter being one of the few allies of President Bashar al-Assad, while the former backs a solution excluding the Syrian leader.
The presence of planes from both Russia and the US-led coalition in Syrian airspace is "fraught with danger," the United Nations warned on Monday.
"What we are seeing now is a lot of different countries and different
coalitions operating in the skies above Syria," UN spokesman Stephane Dujarric said.
"I think it creates a situation that is fraught with danger and very delicate as we had seen on the issue of the violation of airspace with Turkey."
Dujarric stressed that "this really should refocus people's attention to finding a political solution" to the Syrian conflict, which has already killed more than 240,000 people.
Against this backdrop, Syrian activists told Al Jazeera that Russian air strikes have hit areas at the Turkish border.
They reported strikes targeting the northwestern village of Bernas and Oubeen and on Yamadiya displacement camps.
Russia said the aerial campaign, which began on Wednesday, was aimed against the Islamic State of Iraq and the Levant (ISIL) group and other "terrorist organisations".
But Western officials said Russia was failing to distinguish between ISIL fighters and more moderate rebels in Syria.
Russia has also been accused that many of its strikes led to civilian casualties, a claim that Moscow denies.
Source: Al Jazeera and agencies