World News Update, what you need to know

About 30,000 Iraqi troops and militia backed by aircraft have pounded jihadists in and around Tikrit in the biggest offensive yet to retake one of the Islamic State's main strongholds.

ELSEWHERE:

KEROBOKAN - A date to send Myuran Sukumaran and Andrew Chan for execution is imminent, with Bali's prosecutor only waiting on word from Jakarta to start them on their journey to the firing squad.

GENEVA - The US and Russian foreign ministers have expressed cautious optimism after holding talks in Geneva over the fighting in Ukraine, where the UN says more than 6000 people have died in less than a year.

WASHINGTON - Benjamin Netanyahu has warned Washington that an emerging nuclear deal with Iran could threaten his country's very survival, but the Israeli Prime Minister insists relations with the United States remain solid.

MOSCOW - Russian investigators are scrambling to track down the killers of outspoken opposition figure Boris Nemtsov as fresh details emerge about the most shocking political assassination of Vladimir Putin's rule.

NEW YORK - The world's richest person got even richer this year. Forbes says that Bill Gates's net worth rose to $US79.2 billion ($A101.27 billion) in 2015 from $US76 billion last year.

LOS ANGELES - Three Los Angeles police officers shot and killed a man as they wrestled with him on the ground, a confrontation captured on video that millions viewed online.