*Half the production lost in weekend attacks on two key facilities already recovered *Oil prices drop after the sharp rise following the 'drone' strikes

Saudi Arabia said on Tuesday its oil output would be back to normal by the end of the month, with half the production lost in weekend attacks on two key facilities already restored.

Energy Minister Prince Abdulaziz bin Salman, who was only appointed to the role earlier this month, said that the world's top energy exporter had dipped into its strategic reserves to maintain supply to clients.

"I have good news for you...

the oil output to international markets is back to what it was before the attack," he said.

"During the past two days the damage was contained and 50% of the production has been recovered," he added.

"Production will be back to normal by the end of September."

But as the US points the finger of blame at Saudi Arabia's regional rival Iran, the minister — the son of King Salman — refused to be drawn on who was responsible for the Saturday's strikes which roiled global energy markets.

"We don't know who is behind the attack," he said, adding that the kingdom wants "proof based on professionalism and internationally recognised standards".Saudi authorities were also bullish on plans for the mega stock listing of oil giant Aramco, which was thought to be imperilled by the attack.

"The IPO will continue as is, we won't stop anything," said Aramco chairman Yasir al-Rumayyan.

Riyadh pumps some 9.9mn barrels per day (bpd) of which around 7mn bpd are exported, mostly to Asian markets.

The strikes took out half its output, some 6% of global oil production.

Oil prices dropped sharply on Tuesday after the announcement of the Saudi energy minister.

However, the oil market remained on tenterhooks over the threat of retaliation for attacks on Saudi Arabian crude oil facilities on Saturday.

Brent crude futures settled at $64.55 a barrel, down $4.47, or 6.48%.WTI crude futures settled at $59.34 a barrel, down $3.56, or 5.66%.The attacks on crude-processing facilities at Abqaiq and Khurais resulted in the largest single supply disruption in half a century.

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Iran supreme leader says no negotiations 'on any level' with US

Iranian Supreme Leader Ayatollah Ali Khamenei said on Tuesday that no negotiations would take place between Iran and the United States unless the United States "repents," amid a series of accusations flying between the two sides.

If the US "takes back its words and repents and returns to the nuclear deal, which they have violated, they can take part in the meetings of signatories to this agreement with Iran," Khamenei said.

"Otherwise, no negotiation on any level will happen between officials of the Islamic Republic and the US, neither in New York nor anywhere else," he said on state television.

There had been speculation over a possible meeting between Trump and Iranian President Hassan Rouhani on the sidelines of the UN General Assembly in New York, which begins this week.

"I never rule anything out, but I prefer not meeting him," Trump said on Tuesday, according to journalists travelling with the president.