US President Donald Trump

Mr Trump also told NBC News it was his decision alone to sack James Comey.

Mr Comey was leading an inquiry into alleged Russian meddling in the US election and possible collusion between Trump campaign officials and Moscow.

Mr Trump has dismissed the probe as a "charade", a claim directly contradicted by Mr Comey's successor.

In his first interview since firing the FBI director, Mr Trump told NBC News on Thursday he had asked Mr Comey whether he was under investigation.

It is their first encounter since an acrimonious phone call in February.

"We get along great. We have a fantastic relationship, I love Australia, I always have," the AFP news agency quoted Mr Trump as saying.

Protesters also gathered in Mr Trump's home city, the first time he has returned there since his inauguration.

Mr Trump said the two leaders had "reaffirmed ties" between their two countries, and discussed economic, trade, and national security co-operation, as well as migration issues.

His exact intentions remain unclear but the US is reportedly considering a military response.

The BBC's North America editor says a US strike could be imminent.

US Secretary of State Rex Tillerson has said Bashar al-Assad should have no role in a future Syria.

His comments signal an apparent U-turn for the US - only last week the US ambassador to the UN, Nikki Haley, said Washington was no longer prioritising the removal of the Syrian president.

As Trump and President Xi Jinping meet for their first summit, Pyongyang's aggressive pursuit of nuclear and missile expertise will top the agenda. US officials warn that the era of what's known as strategic patience is over.

Theresa May's spokesman, James Slack, said the claim that the UK's signals intelligence agency GCHQ helped then-president Barack Obama eavesdrop on Mr Trump was "ridiculous".

"We've made clear to the administration that these claims are ridiculous and they should be ignored and we've received assurances that these allegations will not be repeated," he said.

Mr Trump accused the National Security Agency (NSA) and FBI of giving out information illegally.

Some US media say top Trump aides were in constant communication with Russian officials during the election campaign.

Intelligence officials previously said they believed Russia tried to influence the vote in favour of Mr Trump.

Moscow has dismissed the claim as unsubstantiated.

Kremlin spokesman Dmitry Peskov said the latest reports of contacts with Trump aides were "not based on any facts".