NATO Secretary General Jens Stoltenberg said there had been a "troubling escalation" in Russian military activity in Syria, after Moscow dramatically expanded its air campaign.
Turkish Prime Minister Ahmet Davutoglu said only two Russian air strikes in Syria had targeted Islamic State jihadists and warned that Ankara would not make any concessions about the security of its borders
Australia will spend Aus$1.3 billion (US$1 billion) on next-generation armoured land vehicles for its army, Prime Minister Malcolm Turnbull said as he announced the latest update to modernise the nation's military.
US Defence Secretary Ashton Carter arrived in Madrid, beginning a European tour amid alarm over Russian bombardments in Syria and the refugee crisis sparked by the conflict.
British Prime Minister David Cameron urged Russian President Vladimir Putin to "change direction" in Syria and recognise that its President Bashar al-Assad must be replaced.
Chechen strongman Ramzan Kadyrov called on the Kremlin to let a contingent from his region fight the Islamic State in Syria, where Russia launched air strikes earlier this week.
Russian air strikes in Syria will last for three to four months and will intensify, a senior Russian lawmaker said as President Vladimir Putin was due in Paris for talks.
NATO General Philip Breedlove expressed concern Monday about the strength of Russia's military build-up in northwestern Syria and the apparent creation of a defensive "bubble" in the Mediterranean.
The United States and Russia could find ways to cooperate on the crisis in Syria, Pentagon chief Ashton Carter said, as Moscow continues a military build-up in the war-torn nation.
Russia's military backing for the Syrian regime only risks sending more extremists to the war-torn country and could further hamper any effort at bringing peace.
Japan's parliament passed contentious security bills into law early Saturday, in a move that could see Japanese troops fight abroad for the first time in 70 years.
Bulgaria began deploying up to 1,000 troops to buttress its southeastern border with Turkey as hundreds of migrants remained stranded for a third day on the Turkish side.
UN Secretary-General Ban Ki-moon voiced outrage after Burkina Faso's presidential guard detained the country's interim president and prime minister, and demanded their immediate release.
Russia wants talks with the US military to ensure their forces do not come into conflict as it continues its build-up in Syria, Secretary of State John Kerry said.
Israeli Prime Minister Benjamin Netanyahu sought Britain's cooperation to "turn back the tide of militant Islam" as he met Prime Minister David Cameron in London.