World powers voiced fears Friday over an imminent all-out assault by President Bashar Assad's forces on Syria's second city Aleppo and called for "maximum pressure" to prevent a new massacre.

France echoed U.S. concerns that Assad was preparing to carry out a slaughter of his own people, and Britain warned that the expected offensive could end in a humanitarian disaster.

U.S. presidential hopeful Mitt Romney tried to put the fuss caused by his criticism of London's Olympic preparations behind him Friday, admitting that the British capital now seems ready for the games.

The Republican challenger, who will face off against President Barack Obama in November's U.S. election, offended many in Britain on Thursday when he began a visit to London by expressing concern about the host city's readiness.

British Foreign Secretary William Hague on Thursday stressed to Prime Minister Najib Miqati his country’s support for Lebanon and inquired about the efforts that are being made by the Lebanese government to aid the Syrian refugees, the premier’s office said.

Miqati is in London to attend the opening ceremony of the 2012 Olympic Games. He is accompanied by Youth and Sports Minister Faisal Karami.

The Olympic flame has had a ride on the London Eye.

Amelia Hempleman-Adams took the torch on a trip on the giant observation wheel on the south side of the River Thames on Sunday, riding atop one of the Eye's viewing capsules as it slowing rotated.

Britain will step up its support for Syria's rebels after Russia and China blocked a U.N. Security Council resolution against Bashar Assad's regime, Foreign Secretary William Hague said Friday.

Hague said Russia in particular would regret its actions, which he said would be harmful to its long-term goals in the region.

Russia on Friday slammed the "unacceptable" Western criticism that followed its decision to block together with China the threat of sanctions against its ally Syria at the U.N. Security Council.

"It is absolutely unacceptable that some Western countries are trying to lay the blame for the escalating Syrian violence on Russia's refusal to support a resolution threatening sanctions against the authorities," foreign ministry spokesman Alexander Lukashevich told reporters.

Regulators are investigating Credit Agricole, HSBC, Deutsche Bank and Societe Generale over the Libor manipulation scandal that claimed the boss of British bank Barclays, the Financial Times reported Thursday.

Citing sources close to the probes, the FT said regulators were examining evidence of links between traders at all four banks and Barclays' former trader Philippe Moryoussef.

World powers said a suicide bombing Wednesday that killed three top Syrian officials showed the urgent need for a political transition.

"The French government, without knowing the circumstances of this attack, has always condemned terrorism. That said, given the level of violence, this makes it even more necessary and urgent to find a political transition," French Foreign Minister Laurent Fabius told the French Senate.

Britain's Tate Modern opens the former power station's giant underground oil tanks as an art space on Wednesday, vastly increasing the capacity of the world's most visited modern art gallery.

The tanks -- which measure 30 meters (100 feet) in diameter and seven meters high and once held one million gallons of oil -- are designed to accommodate giant installations, as well as host performances and projections.

Israel was still holding five foreign women activists on Saturday who were arrested in the West Bank after a demonstration a day earlier, a police spokeswoman said.

"Five European activists arrested Friday during a demonstration in Judea and Samaria (West Bank) remain in detention," Luba Samri told Agence France Presse.