Oil prices extended gains on Monday as efforts to end the Iran war appeared to have stalled, after a nuclear power plant in the United Arab Emirates came under attack and as US President Donald Trump is expected to discuss military options on Iran.

Brent crude futures climbed $1.65, or 1.51%, to $110.91 /bbl by 0703 GMT, but were off the $112 they had touched earlier for their highest since May 5.

US West Texas Intermediate crude stood at $107.42/bbl, up $2, or 1.9%, after a rise to $108.70, its highest since April 30. The front-month June contract expires on Tuesday.

Both contracts gained more than 7% last week as hopes dimmed for a peace deal to end ship attacks and seizures around the key waterway of the Strait of Hormuz.

Last week's talks between Trump and Chinese President Xi Jinping ended without an indication from the world's top oil importer that it would help resolve the conflict unleashed by the US-Israeli attacks on Iran.

Drone attacks on the UAE and Saudi Arabia and rhetoric from the US and Iran raised concerns of an escalation in the conflict.

"These drone strikes are a pointed warning - renewed US or Israeli strikes on Iran could trigger more proxy attacks on Gulf energy and critical infrastructure by Iran or its regional proxies," IG market analyst Tony Sycamore said.

Emirati officials said they were investigating the source of the strike on the Barakah nuclear power plant, adding that the UAE had the full right to respond to such "terrorist attacks".

Saudi Arabia, which intercepted three drones that entered from Iraqi airspace, warned it would take the necessary operational measures to respond to any attempt to violate its sovereignty and security.

Trump is expected to meet top national security advisers on Tuesday to discuss options for military action regarding Iran, Axios reported.

In a move that could support oil prices, the Trump administration on Saturday allowed the lapse of a sanctions waiver that had previously allowed countries including India to buy Russian seaborne oil after a month-long extension.

"Fears of renewed strikes on Iran have worsened supply fears ... the United States letting the Russia sanctions waiver lapse didn't help," said Vandana Hari, founder of oil market analysis provider Vanda Insights.