Republican presidential candidate Jeb Bush vowed on Tuesday to take a more aggressive approach to countering Russia if he is elected president next year, calling Vladimir Putin an "agile adversary" who is exploiting a vacuum of U.S. leadership in Syria and elsewhere.

In an interview with Reuters, Bush said that if elected in 2016 he would seek to build a coalition of European and Arab partners to work for the ouster of Syrian President Bashar al-Assad, which he said is key to resolving the festering conflict and a worsening refugee crisis.

Calling Putin a "bully," Bush said the United States and Europe should also extend sanctions against Moscow over its military aggression in Ukraine that are set to expire at year's end.