Just weeks after crude prices had fallen on hopes that the Middle East was easing, oil has staged a sharp comeback. Fresh attacks on Saudi oil tankers in the Red Sea and a disruption to Kazakhstan's exports have revived fears over global supplies, sending prices beyond the $100-a-barrel mark.On Friday, Brent crude futures fell 63 cents, or 0.63%, to $100.1 a barrel, while US West Texas Intermediate (WTI) crude slipped 69 cents, or 0.75%, to $91.50 a barrel. Despite the decline, Brent remained on track for a 13.5% weekly gain, while WTI was set to rise 10.9%.In the previous session, Brent settled 7% higher and WTI gained 6.2%. Brent also closed above $100 a barrel for the first time since May and touched $102 during the session, its highest level since then.Red Sea attacks shake oil marketsThe latest rally comes after Iran-aligned Houthi rebels said they had attacked two Saudi oil tankers in the Red Sea.The attacks raised concerns that the Bab el-Mandeb shipping route, which links the Red Sea to the Indian Ocean, could face disruptions. The passage is the world's second most important oil shipping route after the Strait of Hormuz.Earlier this week, the Houthis announced a naval blockade on Saudi Arabia, which had been sending oil through pipelines to bypass Iran's closure of the Strait of Hormuz.Iran had been urging the Houthis to close the Bab el-Mandeb gateway if the United States continued attacking Iranian power infrastructure after an interim truce between the two countries collapsed two weeks ago.US President Donald Trump said he would "hold Iran responsible" for any further attacks. He also warned of "major military punishment" against the Houthi rebels in Yemen if they continued attacking ships."The noose around global energy supply routes is pulling tighter again," IG market analyst Tony Sycamore said in a note.Kazakhstan adds to supply concernsAt the same time, fresh worries emerged from Kazakhstan, where oil companies temporarily cut production after suspected Ukrainian drone attacks forced the closure of the country's main Black Sea export terminal.Industry sources said the Caspian Pipeline Consortium stopped receiving oil from Kazakhstan after suspending loadings because of attacks on tankers at the terminal. The route carries about 2% of global daily crude supply.Kazakhstan's energy ministry did not say how much production had been reduced, but one source said output at the country's biggest oilfield had been cut by more than half.The latest jump in crude prices marks a sharp reversal from a few weeks ago, when Brent had slipped below $72 a barrel on hopes that the conflict involving the United States, Israel and Iran was easing and that the Strait of Hormuz would fully reopen.