BOGOTA, Colombia (CNN) -- Colombian President Andres Pastrana said Monday that Cuban leader Fidel Castro could play a "very important" role in brokering a peace agreement to end a long-standing guerrilla war between his government and Marxist rebels.

The two leaders will meet later this week at the Non-Aligned Movement summit in Durban, South Africa.

"It will be our first direct talks," said Pastrana, who took office August 7. "I think the part that Cuba can play in the country's peace process is very important."

Castro is widely revered by Colombia's two largest Marxist rebel groups, the Revolutionary Armed Forces of Colombia (FARC) and the Cuban-inspired National Liberation Army (ELN).

The idea was first suggested last November by Pastrana's predecessor, Ernesto Samper, during the Ibero-American summit in Venezuela.

"If it were in my hands to do something for peace, I would do it as a basic duty," Castro said then.

Samper's peace overtures were shunned by the rebels, who called his government "illegitimate" because of charges he bankrolled his election with drug money.

Pastrana was elected to office earlier this year in part because of a campaign promise to end the three decades of conflict, fought mostly in the southern and eastern jungles of Colombia.

He also promised to demilitarize a large swath of those areas in preparation for peace talks.

It is not yet known if Pastrana will seek Castro's direct mediation in the peace talks.

Meanwhile, the Cuban president, on a private visit to Brazil on Monday, called for a complete overhaul of the United Nations.

"It needs to be rebuilt, starting with the very first stone," he said in response to a question about reform in the international diplomatic body.

Castro, in the northeastern city of Salvador, did not elaborate on his statement, insisting he "did not come here to talk about politics."

But the 72-year-old Cuban leader recently criticized the power given to the U.N. Security Council's five permanent members.

Cesar Borges, governor of Bahia state where Castro was visiting, said the Cuban leader supports "Brazil securing a seat on the Security Council."

Castro was visiting his friend, Antonio Carlos Magalhaes, one of Brazil's top political leaders. He was scheduled to depart Monday evening for a stopover in Namibia before attending the South African summit.

Castro first met Magalhaes in 1987, when he traveled to Havana as Brazil's Communications minister. Cuban and Brazilian officials say Castro has since visited Salvador three times and is very fond of the region's Afro-Brazilian cuisine.

Castro canceled plans to attend a samba-reggae concert downtown, where he was expected to receive a warm reception.

A similar welcome seems likely when Castro arrives in Durban later this week.

A long-time supporter of President Nelson Mandela's African National Congress during its struggle against white rule, Castro has been a popular figure in South Africa for many years.

During the 1970s, he sent Cuban troops to Angola, where they fought rebels supported by South Africa's apartheid government. In turn, the ANC has publicly called for an end to a 36-year-old economic embargo on communist Cuba.

Castro is expected to stay in South Africa after the conclusion of the summit. He is scheduled to address the South African parliament in Cape Town and visit Robben Island, where Mandela was jailed for 27 years because of his opposition to apartheid.

What remains unclear is whether Mandela will raise the issues of democracy and human rights with his Cuban friend.

Reuters contributed to this report.