- Leaders worry assault may destabilise peace efforts in Syria, cause a humanitarian catastrophe and reignite Islamic State (IS) group.
- EU chief Jean-Claude Juncker called for a political solution to end the Syrian conflict, telling Ankara the bloc would not pay for any so-called "safe zone" that might be created.
- Russian President Vladimir Putin urged his Turkish counterpart President Recep Tayyip Erdogan to "think carefully" before taking any action "so as not to harm overall efforts to resolve the Syrian crisis."
World governments reacted with concern Wednesday after Turkey launched a military offensive on Kurdish forces in northern Syria, while the UN Security Council plans to hold an emergency meeting to discuss the assault.
Here are some of the initial comments following the start of the attack, called "Operation Peace Spring".
NATO chief Jens Stoltenberg urged Turkey to show "restraint", while acknowledging that Ankara had "legitimate security concerns".
"It's important to avoid actions that may further destabilise the region, escalate tensions, and cause more human suffering," Stoltenberg said at a news conference in Rome, in remarks released by his office.
The UN Security Council's president, South African ambassador Jerry Matthews Matjila, also appealed to Turkey to "protect civilians" and exercise "maximum restraint".
US President Donald Trump on Wednesday called the incursion into northern Syria a "bad idea".
VERY BAD IDEA
He insisted Washington "does not endorse this attack", despite having withdrawn US troops from the area in what was interpreted as a green light for Turkey to assault Kurdish militias previously allied with America.
Earlier this week, Trump said he would "obliterate" Turkey's economy if it went too far.
The US and the UK also expressed concern over the risk of a humanitarian catastrophe in the region.
Ahead of the launch of the offensive, Russian President Vladimir Putin urged his Turkish counterpart President Recep Tayyip Erdogan to "think carefully" before taking any action "so as not to harm overall efforts to resolve the Syrian crisis," the presidency said following a phone call between the two leaders.
Erdogan for his part told Putin that the offensive "will contribute to Syria's peace and stability and ease the path to a political solution".