* SPDR posts biggest one-day percentage gain since 2008
* Speculators increase net longs in COMEX gold
* Spot gold prices up nearly 8% so far this month (Updates prices, adds comments)
June 24 (Reuters) - Gold climbed on Monday as the dollar sagged, with bullion prices hemmed near a six-year high scaled in the previous session as tensions between the United States and Iran fuelled safe-haven buying.
Spot gold jumped 0.6% to $1,408.23 an ounce by 10:53 a.m. EDT (1453 GMT), heading for a fifth straight session of gains. Gold prices hit $1,410.78 on Friday, their highest since early September, 2013.
U.S. gold futures rose 0.8% to $1,411.80 an ounce.
"It's the strong upside momentum from last week along with higher ETF buying and a weaker dollar boosting gold prices today," INTL FCStone analyst Edward Meir said.
Holdings of the world's largest gold-backed ETF, SPDR Gold Trust, jumped 4.6% on Friday from a day earlier, its biggest one-day percentage gain since September 2008.
Helping gold's appeal, the dollar dipped, having faced its biggest weekly drop since mid-February on bets the U.S. central bank would start lowering interest rates as early as next month.
The U.S. Federal Reserve and the European Central Bank last week hinted that they were open to easing policy to counter a global economic slowdown, exacerbated by global trade tensions.
Lingering geo-political uncertainties in the Persian Gulf are also providing support to gold prices, Meir added.
U.S. President Donald Trump said on Sunday he was not seeking war with Tehran, but tensions remain high between the longtime foes, with Washington due to announce "significant" sanctions on Iran on Monday.
The market's focus now shifts to whether Washington and Beijing can resolve their trade dispute at a summit in Japan this week of leaders from the Group of 20 leading world economies.
"The China-U.S. trade conflict is not getting anywhere. Additionally, the Iranian conflict is also starting to heat-up... That is why people are seeking gold as safe haven," said an analyst based in New York.
"The climb in gold prices have woken people up. Breaking over $1,400 was a significant psychological factor. Now that gold has broken the 1,400 level, it is expected to go up."
Gold prices have risen nearly 8% so far this month, and more than $70 just over the past week.
Speculators also boosted their bullish stance in COMEX gold in the week to June 18 and switched to a net long in silver futures and options, the U.S. Commodity Futures Trading Commission said on Friday.
Silver edged 0.1% higher to $15.37 per ounce and platinum was up 0.5% at $809.71.
Palladium climbed 1.6% to $1,523.28 an ounce. (Reporting by Diptendu Lahiri and Swati Verma in Bengaluru Editing by Marguerita Choy)