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... Iran's move to change the venue and agenda for the talks, scheduled for Friday in Istanbul, comes amid heightened tensions as the US builds up forces in the Middle East.

Regional players have pushed for a resolution of a standoff that has led to mutual threats of air strikes and stirred fears of escalation into a wider war.

The US military on Tuesday shot down an Iranian drone that "aggressively" approached the Abraham Lincoln aircraft carrier in the Arabian Sea, the US military said, in an incident first reported by Reuters.

US President Donald Trump, who warned on Monday that "bad things" would probably happen if a deal could not be reached with Iran, told reporters at the White House on Tuesday: "We are negotiating with them right now." He did not elaborate and declined to say where he expected the talks to take place.

The regional diplomat with knowledge of Iran's demands said Tehran sought "to change the format, they want to change the scope." ...