VIENNA — Iran and world powers are unlikely to strike a deal this week that would lift international sanctions in exchange for a cut in the Persian Gulf nation’s nuclear activities, according to a former White House adviser.

“I don’t expect there to be an agreement, certainly not before the presidential elections in Iran in June,” Gary Samore, who advised President Barack Obama on nuclear non-proliferation and arms control until January, said. “There may be some incremental progress in terms of a slight narrowing of big differences but I don’t think it will come to an agreement.”

Negotiators from the so-called P5+1 — comprised of China, France, Germany, Russia, Britain, and the United States — meet their Iranian counterparts April 5 in Almaty, Kazakhstan.

Iran, with the world’s fourth-biggest proven oil reserves, said the sides narrowed differences after their last meeting. Tehran’s government is under dozens of international sanctions targeting its energy, financial and nuclear industries.

“Both sides are trying to build up bargaining leverage,” said Samore, who spoke on a Brookings Institution panel. “We haven’t reached the point yet where some point of agreement to relax the sanctions and the nuclear activities is possible.”

The talks are being complicated by Iran’s presidential election, pressure by Israel and the Syrian insurrection against President Bashar al-Assad, according to Javier Solana, who led the European Union’s negotiations with Iran until 2009, and joined Samore on the panel.

“I don’t think it will be possible to move on Iran without solving Syria,” Solana said. “They have a very intense relationship. Without solving that problem, it will be very difficult to get the negotiation moving.”

“The collapse of Assad makes a nuclear deal more likely,” Samore said. Iran “would feel more isolated, under greater pressure, more likely to make tactical concessions.”

The United Nations estimates at least 70,000 Syrians have been killed in two years of fighting that has displaced millions.