In a joint statement, the trio agrees to coordinate efforts to ensure Syria's security and stability after a trilateral summit in the Turkish capital, Ankara.
The explosion happened near a local hospital in Cobanbey town. No group has yet claimed responsibility for the attack.
The Syrian Observatory for Human Rights reported "around 3,000 people" returned to the northern Hama and the southern Idlib countryside from other areas under regime control.
Syrian regime and Russian forces have killed at least six civilians in northwestern Idlib province, according to a war monitor.
The opposition and rebel withdrawal came after the Russia-backed Syrian regime forces advanced into Khan Shaykhun city in Idlib. The US urged the regime to revert to a ceasefire in Idlib after Monday's air strike on a Turkish convoy.
As the Syrian regime battles the last rebel stronghold, could it begin to release those detained in inhumane conditions since the beginning of the conflict?
The push towards Khan Shaykhun threatens to encircle the last remaining pocket of opposition and rebel territory in neighbouring Hama province, including the towns of Morek, Kafr Zeita and Latamneh.
The capture of Habeet opens up an approach to southern regions of Idlib, which is home to some three million people, many of them displaced by fighting in other parts of the country.
"We will never withdraw from the zone," says Hayat Tahrir al Sham, the largest militant group in northwestern Idlib, two days after regime announced a truce between it and opposition forces.
The regime offers to halt its offensive if opposition withdraws fighters and weaponry from a buffer zone in northern Syria.
Months after the start of the offensive and despite heavy bombardment, Assad regime fighters have failed to make significant advances against a determined opposition force.
The US request comes after Trump has repeatedly urged Berlin to increase its defence spending, last month calling Germany "delinquent" over its contributions to NATO's budget.
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