* Graphic: World FX rates in 2019 http://tmsnrt.rs/2egbfVh
By Saikat Chatterjee
LONDON, Aug 29 (Reuters) - The Japanese yen edged higher on Thursday, heading for its biggest monthly rise since May as risk appetite remained on the back foot with investors sceptical on the prospect of a trade-war breakthrough any time soon.
"Investors are still concerned about the trade war and there is little optimism we will see a substantial breakthrough in negotiations," said Esther Maria Reichelt, an FX strategist at Commerzbank.
U.S. President Donald Trump's administration on Wednesday made official its extra 5% tariff on $300 billion in Chinese imports and set collection dates of Sept. 1 and Dec. 15.
Against the greenback, the yen edged 0.2% higher at 105.83 yen. For the month, it is set to gain 2.5% against the dollar, putting it on track for its biggest monthly rise in three months.
"It's very difficult to take on any kind of major risk in this environment," said Chris Weston, head of research at forex brokerage Pepperstone Group, pointing to the inverted yield curve as an indicator of sentiment.
Spreads between 10-year U.S. Treasury debt and comparable two-year bond yields inverted to minus 3 bps, its lowest since May 2007.
Sterling remained in the spotlight after Prime Minister Boris Johnson's plan to suspend parliament raised the odds of a no-deal Brexit. The British currency edged a quarter of percent lower at $1.2183, approaching a January 2017 low below $1.2015.
China's onshore spot yuan eased slightly to be weaker for an 11th straight session, although a firmer-than-expected central bank fixing helped stem deeper losses. Against a basket of currencies, the dollar was steady around 98.190.
Elsewhere, the kiwi was off 0.3% at $0.6318, after touching its lowest since September 2015 at $0.6311. (Reporting by Saikat Chatterjee Editing by Mark Heinrich)