US President Barack Obama has arrived in Australia for a twice-delayed visit expected to focus on security ties.

美国总统奥巴马抵达澳大利亚——此次访问曾被推迟两次——期望与其加强安全联系。

The two countries have a decades-long security alliance
He landed in the capital, Canberra, where he was greeted by Prime Minister Julia Gillard.

On Thursday he will speak to parliament before travelling to Darwin to visit a military base.

The visit comes as the two countries mark a 60-year security alliance, and they are expected to announce plans for expanded military co-operation.

The visit also coincides with what is being seen as a US push to refocus on allies within the Asia-Pacific region as a counterbalance（平衡力） to China.

The US president flew in from this weekend's Asia-Pacific Economic Co-operation (Apec) forum¹ in Honolulu.

After talks, he and Ms Gillard will give a joint² news conference and then have dinner together.

Mr Obama's speech to parliament on Thursday is expected to be the key engagement of his visit.

He is expected to set out plans for greater US engagement in the region.

Later in Darwin, he will visit a memorial to honour US and Australian soldiers killed during World War II.

It will be the first visit to Darwin by a US leader.

Reports say that while Mr Obama is there, the two sides will announce more joint training exercises in the Northern Territory and increased US access to Australian bases.

Australian Defence Minister Stephen Smith said expanding co-operation was an "important, practical" step.

"What we have in contemplation（沉思，注视） is greater utilisation（使用，利用） of access to facilities, greater training, greater exercises. It will effectively be a continuation and expansion of what we currently do," he told Australia's ABC News.

Mr Obama has twice cancelled visits to Australia in the past - in March 2010 as he worked to pass healthcare reform legislation and then in June the same year amid the Gulf³ of Mexico oil spill.

After his stop in Darwin, Mr Obama flies to Indonesia for a summit of Asian leaders.