A US service member was killed and several other people were injured when a military helicopter on a mission against Islamic State militants crashed in Iraq.

US First Lady Melania Trump renewed her campaign to tackle cyber bullying on Monday, as her husband lit up the internet with a stream of invective against his perceived foes.

When asked about Trump's tweet, Bolton also mentioned Beijing, which is currently at an impasse with Washington on trade talks.

The Ghanaian national was a career diplomat who projected quiet charisma and was widely credited for raising the world body's profile in global politics.

The United States on Friday imposed sanctions on four Myanmar military and police commanders and two army units for involvement in what it called "ethnic cleansing" and other human rights abuses against the country's Rohingya Muslims, the Treasury Department said.

The lira gained some support from the announcement late on Wednesday of a Qatari pledge to invest $15bn in Turkey.

Andrew Brunson, who faces 35 years in jail over terror and espionage charges, will remain under house arrest.

The move comes after US President Donald Trump announced that the United States was doubling steel and aluminium tariffs on Turkey.

Relations between the two Nato allies have plummeted in one of their worst crises in decades after the detention of US pastor Andrew Brunson on terror-related charges.

The United States has vowed to develop a new "Space Force" that would give America dominance over rivals in China and elsewhere.

Ayatollah Ali Khamenei's comments add to the pressure on President Hassan Rouhani following a collapse in the currency and widespread protests over high prices and corruption.

Turkish President Recep Tayyip Erdogan on Sunday slammed the crash of the lira amid a widening spat with the United States as a "political plot" and said his country would instead seek new markets and new allies.