The BRIC nations -- Brazil, Russia, India and China -- are set to wrestle with international pressure to back sanctions against Iran when they hold the second-ever summit in Brazil at the end of the week.

The diplomatic issue is expected to be raised at the Friday gathering in Brasilia, along with other matters involving the four countries, which together represent 40 percent of the world's population and which have emerged as an increasingly powerful bloc on emerging economies.

The meeting is sandwiched between a Washington summit early this week on nuclear security, and a looming UN Security Council vote on whether to broaden sanctions against Iran over its nuclear program.

The United States, Britain, France and Germany have been urging the BRICs to support sanctions against Iran.

Most attention in the lead up to the UN vote, expected within weeks, is likely to be on the UN Security Council members.

Britain, China, France, Russia and the United States are the five permanent council members whose power of veto mean they must support or at least abstain on any sanctions resolution.

Brazil is a temporary UN Security Council member with no veto power, but it is one of Iran's biggest defenders at the world body's top table -- and therefore the focus for lobbying by the Washington and other Western capitals.

Thus far, Brazilian President Luiz Inacio Lula da Silva has shown no sign of acquiescing, even after a trilateral meeting with US President Barack Obama and Turkish Prime Minister Recep Tayyip Erdogan on Tuesday.

Lula, who hosted a visit by Iranian President Mahmoud Ahmadinejad last year and who is scheduled to travel to Iran next month, has resolutely stood by Tehran's assertion that it has a right to atomic energy.

The United States and European Union countries claim that Iran is embarking on a quest for nuclear weapons and can only be forced to negotiate on the issue by tougher sanctions.

Friday's BRIC summit will see Lula sit down with his Chinese and Russian counterparts, Hu Jintao and Dimitri Medvedev, and Indian Prime Minister Mamohan Singh to thrash out common ground on several issues.

Also on the agenda: reforming international institutions such as the International Monetary Fund and World Bank to give greater prominence to emerging powers, said Roberto Jaguaribe, the Brazilian official organizing the summit.

The BRIC nations together accounted for nearly half the world's growth this decade, and 16 percent of the world's economic output, according to the IMF.

With the exception of Russia, the grouping also handled the global recession in relatively good shape.