"We stand in solidarity with all Australians. Our thoughts and prayers are with all those affected by the Sydney siege yesterday," he said in his Twitter update today.
The seige began at 9.45am when a gunman burst into the cafe and took 17 people hostage.
The tense 16-hour crisis ended when heavily-armed policemen stormed the cafe, resulting in the death of the gunman identified as Man Haron Monis, 50.
Two hostages were killed and four others were injured.
The hostages were barrister and mother of three Katrina Dawson, 38, and cafe manager Tori Johnson, 34.
