Demonstrations calling for the closure of Guantanamo Bay occurred around the world on Sunday. Amnesty International, the international rights organisation, held a protest outside the US embassy in Madrid, the Spanish capital, calling on Obama to investigate allegations of abuse at the prison.
Rallies also took place in Montreal, London and Lima, in Peru.
In Washington DC organisers of a protest said that 60 protesters had also begun a nine-day fast in support of Obama keeping his promise to close the prison.
The Cuba-based camp, which has been widely criticised amid reports of inmates being tortured and abused, was opened in 2002 to hold prisoners captured during the Bush administration's so-called "war on terror" in Afghanistan and Pakistan.
Among problems to be dealt with are how the US legally resolves ongoing military tribunals and the fate of about 60 detainees that US officials have approved for transfer to their home countries, Obama said.
'Heartbreaking' war on Gaza
During Sunday's interview, he was asked for his response to criticisms of his silence on Israel's war on Gaza, which many in the Arab world have interpreted as callousness.
He said he stood by comments he made in July supporting Israel's "right to defend itself," adding: "When you see civilians, whether Palestinian or Israeli, harmed, under hardship, it's heartbreaking.
"[But] we cannot have two administrations at the same time simultaneously sending signals in a volatile situation."
He said he was creating a team to handle the Middle East conflict "as a whole" once he takes office on January 20, that would "be engaging with all of the actors there ... [and] work to create a strategic approach that ensures that both Israelis and Palestinians can meet their aspirations".
His comments came shortly before Ehud Olmert, the Israeli prime minister, said for the first time on Sunday that Israel was "nearing the goals that it set for itself" in its war on Gaza, amid some of the heaviest clashes of an offensive that has killed nearly 900 people in the territory, nearly half of them believed to be women and children.
|Demonstrators in the US have asked Obama to push for a ceasefire in Gaza [GALLO/GETTY]
Obama said he would seek much broader engagement with Iran, in a shift from the administration of George Bush, the US president.
The new approach would include "sending a signal that we respect the aspirations of the Iranian people, but that we also have certain expectations in terms of how an international actor behaves," he said.
Obama has said he was prepared to offer Iran economic incentives to stop its nuclear work but warned tougher sanctions could be imposed if it refused.