The secretary general of the OPEC oil exporting group said that it would difficult to replace the crude output of Iran if the country was attacked, in comments published on Thursday.

"If somethng happened in Iran, it is difficult to replace 4.1 or 4.2 million barrels a day," Abdallah el-Badri told the daily newsletter of the World Petroleum Congress here, referring to Iran's daily output.

"The price (of crude) of course will go up."

Oil surged past 145 dollars per barrel for the first time on Thursday on the weak US dollar and Middle East tension.

Asked about fears that Iran would close the straits of Hormuz if attacked, a key shipping route through which 40 percent of Middle Eastern oil pass, he replied: "When you are in a war, you are in a war. You can use anything."

There has been a surge in speculation recently that Israel might be planning a military strike against Iran's nuclear sites after it emerged that Israeli fighter planes had carried out practice runs.

Iran has been locked in a five-year standoff with the West over its nuclear programme, which it says is for generating electricity while Western powers fear the development of nuclear weapons.

"Iran, if there were any kind of activity of any sort, is not going to be quiet and would react fiercely," Iranian Oil Minister Gholam Hossein Nozari said here when asked what Tehran would do in the event of an attack.

The Organization of Petroleum Exporting Countries (OPEC) has been under pressure from consumer countries to increase supplies to lower prices, but members contend that supply is not the cause of 145-dollar oil.