Libyan and US officials say hundreds of Russian mercenaries are backing commander Khalifa Haftar, whose forces have been trying for months to capture the capital Tripoli.
Earlier, the rebels announced they would release 350 prisoners, including three Saudi Arabians, under UN's supervision as part of peace initiative.
The education of a further 3.7 million children at risk as teachers' salaries have not been paid in more than two years, UNICEF warns in a statement.
Several others were wounded during clashes in Yemen's second city Aden as violence flares between pro-government fighters and those seeking an independent south.
China and India have a long history of territorial disputes along their shared border. Beijing says India has undermined China's territorial sovereignty by revoking Article 370 unilaterally.
A Yemeni health official says that along with the 51 killed, as many as 56 were wounded in Thursday's attacks.
The war in Syria, now in its eighth year, has seen children paying the heaviest price. At least 33 have been killed since June this year, compared to 31 children during the entirety of 2018.
More than 400,000 people have been displaced in northwestern Syria over the past three months, the UN, as the regime presses an intensified bombardment of the rebel-held region.
Even though he was just in his 20s, the young Syrian captured images of the aftermath of atrocities committed by the regime and Russian forces until he died in the line of duty.
Moscow noted the transfer of 540 military contractors in June alone and says the mercenaries are tasked with protecting oil facilities and training militants loyal to the US.
As part of the "phase one" of a ceasefire, the Houthi movement's unilateral withdrawal from the key ports began on Saturday, in the most significant advance yet for efforts to end the four-year-old war and relieve hunger.
Ukrainian comedian and presidential candidate Volodymyr Zelenskiy is heading to Paris to meet the French president. He is predicted to win the presidential election run-off, despite his only political experience of playing the president in a TV show.
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