A Hillsborough County Sheriff's motorcycle following an accident while escorting US President Barack Obama to a speech about trade policies with Latin America at the Port of Tampa in Tampa, Florida, April 13, 2012.

US President Barack Obama walks on the South Lawn upon returning at the White House in Washington, DC, on April 27, 2012 after visiting with US troops at Fort Stewart in Georgia.

US President Barack Obama and his wife Michelle walk from Marine One to the White House in Washington.

German Chancellor Angela Merkel is welcomed by U.S. President Barack Obama at the G8 summit in Camp David, May 18, 2012.

US President Barack Obama disembarks from Marine One at the White House in Washington on May 5, 2012

U.S. President Barack Obama (R) greets French President Francois Hollande as he arrives at the G8 Summit at Camp David, Maryland May 18, 2012.

US President Barack Obama and First Lady Michelle Obama take part in a ceremony May 28, 2012 at the Vietnam War Memorial in Washington, DC. The Memorial Day event also marks the 50th anniversary of the start of the Vietnam War.

April 18,, 2012 in Elyria, Ohio. President Obama speaks to residents of Lorain County, Ohio at Lorain County Community College during a campaign stop in the state.

U.S. President Barack Obama and his daughter Sasha step off Air Force One in Chicago June 15, 2012. The first family arrived in their hometown for the Father's Day weekend.

New World Bank President Jim Yong Kim leaves a hotel in Lima, April 16, 2012.

U.S. President Barack Obama steps out from the Marine One helicopter on the South Lawn of the White House upon his return to Washington May 2, 2012 after a trip to Afghanistan.

A Syrian women inspects the destruction at her house in the Bab Amro neighbourhood of Homs on May 2, 2012.

A Syrian man inspects a damaged house in Talbisa area in Homs, northern Syria April 10, 2012.

Firefighters spray water on a burning fuel tanker in Kabul April 23, 2012. The cause of the blaze is unknown and police are investigating.

A picture shows damaged buildings in Bayyada neighbourhood in the central province of Homs.

A view of destroyed portion of a classroom roof at a private school after roof collapse incident in Kotri on Tuesday, April 17, 2012.

A handout picture released by the Higher Committee for the Syrian Revolution on April 11, 2012 shows a burnt out cot in a house destroyed by conflict in the town of Dael in the southern Syrian province of Daraa.

Pakistani relatives of the the plane crash victims mourn at the airport in Karachi on April 20, 2012. Up to 130 people are feared dead after a Boeing 737 crashed while trying to land in bad weather near the Pakistani capital Islamabad on April 20, officials said.

A handout picture released by the Higher Committee for the Syrian Revolution on April 11, 2012 shows a boy holding a burnt out bicycle in a house destroyed by violence in the town of Dael in the southern Syrian province of Daraa.

A view of a home after part of its exterior was destroyed after a tornado hit Thurman, Iowa April 15, 2012.

A Syrian girl reads a book in her damaged house in Talbisa area in Homs, northern Syria April 10, 2012.