London: Oil was below $138 a barrel on Tuesday after an earlier advance in response to a rumoured attack on Iran's nuclear facilities, which was denied.

"This is just a rumour. No attack against Iran's nuclear facilities has taken place," a senior Iranian nuclear official said.

US crude for August delivery was up 68 cents at $137.42 a barrel by 1453 GMT, after settling up $1.38 on Monday. It hit a record high of $139.89 on June 16. London Brent crude was up 73 cents at $136.64 a barrel.

Tension over Iran's nuc-lear programme has played a big part in oil's rise to record levels near $140 a barrel.

The European Union this week imposed new sanctions on Iran, including an asset freeze on its biggest bank.

Analysts are worried heightened tensions between Iran and the West could threaten the Straits of Hormuz, which separating Iran from the Arabian Peninsula through which roughly 40 per cent of the world's traded oil flows.

The United Nations will seek a 90-day truce with militants that have attacked oil facilities in the oil-producing Niger Delta. Supply disruptions in Nigeria have helped push US crude up by more than 40 per cent this year.