The French left votes Sunday in the second round of France's first U.S.-style primary, called to decide who will take on Nicolas Sarkozy as the Socialist candidate in next year's presidential election.

Facing off for the prize are 57-year-old lawmaker and former Socialist Party chief Francois Hollande, the frontrunner, and Martine Aubry, another party leader who gave France the 35-hour working week when labor minister.

A truck carrying copper collided with a bus in Zambia on Saturday, killing 18 people, police said.

The accident took place north of Lusaka in Kapiri Mposhi, police spokeswoman Ndandula Siamana told Agence France Presse. The bus was on its way to the capital.

Seventy people were injured in violent clashes in Rome on Saturday that broke out at an anti-capitalist protest, with three in a serious condition, Italian news agency ANSA reported.

Twenty-five were treated at a field clinic near St John Lateran square where most of the clashes between protesters and police occurred. The 45 others were taken to other emergency wards in Rome, the report said.

Opposition parties in Liberia on Saturday said they were pulling out of the elections, claiming fraud, as vote-counting put incumbent President Ellen Johnson Sirleaf in the lead.

"We are pulling out of the process because it is not democratic and there is a lot of fraud," an opposition source said in the wake of the October 11 elections which also included parliamentary and senatorial polls.

President Dmitry Medvedev on Saturday denied that Vladimir Putin's expected return to the Kremlin would throw Russia back to its past but admitted the decision disappointed some of his supporters.

Lampooned by liberals as a lame duck who had failed to change Russia in his presidency, Medvedev sought to regain the initiative in a town hall-style meeting with supporters at the trendy Red October complex in central Moscow.

Russia's ruling party on Friday formally confirmed Prime Minister Vladimir Putin as its candidate for the March 2012 presidential election.

"United Russia proposes its leader, the party leader, Vladimir Vladimirovitch Putin, for the post of president of Russia," the party said in an address published on its website.

Militants tried to blast their way into an American base in eastern Afghanistan on Saturday, striking before dawn with rocket-propelled grenades and a vehicle packed with explosives.

The attackers failed to breach the gate of the base in Panjshir province's Rakha district, though they did hit a security tower with a rocket-propelled grenade, said provincial Police Chief Gen. Mohammad Qasim Jangalbagh.

A U.S. drone strike targeting a militant compound in a Pakistani tribal region killed four rebels in the fourth attack in two days near the Afghan border, security officials said Saturday.

The drones fired eight missiles Friday night at the compound in Baghar, 40 kilometers (25 miles) west of Wana, the main town of South Waziristan tribal district, where the military launched a ground offensive two years ago.

U.S. President Barack Obama said Friday he is sending 100 combat troops to central Africa to help and advise forces battling the Ugandan Lord's Resistance Army rebels accused of gross human rights abuses.

"These forces will act as advisers to partner forces that have the goal of removing from the battlefield Joseph Kony and other senior leadership of the LRA," Obama said, but warned they would not lead the fighting themselves.

British Defense Secretary Liam Fox resigned Friday amid a spiraling scandal over his links to the best man at his wedding, becoming the first Conservative minister to quit the coalition government.

Fox, 50, who played a key role in Britain's military campaigns in Libya and Afghanistan, stepped down after it emerged that his friend Adam Werritty posed as a government adviser and took a string of foreign jaunts with the minister.