Saudi activists have urged women to defy a traditional driving ban and get behind the wheel on Saturday, the second day of a visit by U.S. President Barack Obama.

"We have fixed a day every month to pursue our campaign," activist Madiha al-Ajroush told Agence France Presse Friday, insisting that it was a coincidence their latest protest and Obama's visit came on the same day.

U.S. President Barack Obama sought Friday to allay Riyadh's criticism of his policies on Syria and Iran, telling the Saudi king their two countries remain in lockstep on strategic interests.

He also assured King Abdullah that the U.S. "won't accept a bad deal" with Iran, as global powers negotiate a treaty reining in Tehran's controversial nuclear program.

U.S. President Barack Obama in an interview aired Friday said Russia must "move back" its troops from the Ukraine border and start negotiating.

Obama told CBS News that Russian President Vladimir Putin's decision to assemble forces on the border may "simply be an effort to intimidate Ukraine, or it may be that they've got additional plans."

U.S. President Barack Obama took time out during his trip to Rome for a half-hour private guided tour of the Colosseum, saying he was amazed by the size of the ancient Roman amphitheater.

The Colosseum and the Roman Forum were entirely closed to the public during the visit in which Obama was accompanied by red-headed Barbara Nazzaro, technical director of the Colosseum.

Italian Prime Minister Matteo Renzi on Thursday told U.S. President Barack Obama he looked to him as "a source of inspiration and a model" and would apply his "Yes we can" slogan to Italy.

"President Obama is not only the president of the United States, obviously, but for me and my team a source of inspiration and a model," Renzi said at a joint press conference with Obama.

A former wife of Saudi Arabia's King Abdullah appealed to U.S. President Barack Obama on Thursday for help in the case of four daughters she says are being held in a royal palace.

Alanoud AlFayez, 57, a Jordanian national who has lived in London since her divorce from the Saudi monarch in 2003, said her children needed to be "saved".

Pope Francis on Thursday defended the Catholic Church's anti-abortion stance and discussed immigration reform at a historic first meeting with President Barack Obama, whose health law has incensed Catholic leaders.

The Vatican said the two sides had discussed "the exercise of the rights to religious freedom, life and conscientious objection", foiling White House hopes of public Vatican support for Obama's anti-poverty agenda.

Dozens of U.S. lawmakers have urged President Barack Obama to publicly address Saudi Arabia's "systematic human rights violations" when he visits the kingdom Friday.

With their decades-old alliance fraying amid tensions over Washington's efforts to reach a nuclear deal with Iran and its reluctance to engage more forcefully in Syria, regional issues are expected to take precedence when Obama meets with King Abdullah on the U.S. leader's second visit to Riyadh since taking office in 2009.

President Barack Obama put forward a plan Thursday to end bulk collection of telephone records, aiming to defuse a controversy over the government's sweeping surveillance activities on millions of Americans.

In measures taken in response to a global outcry over the National Security Agency's eavesdropping programs, Obama said telephone companies would be required to hold data for the same length of time they currently do, while allowing government agencies to access it with court approval.

Barack Obama will meet Pope Francis for the first time Thursday for talks on a shared agenda to fight inequality which the U.S. President hopes will help boost support at home.

The talks between the first Latin-American pope and first African-American U.S. president will focus on tackling the gap between the rich and the poor, but are likely to spill over into thornier issues such as abortion, homosexuals and contraception.