By Sune Engel Rasmussen in Beirut and Aresu Eqbali in Tehran 

Iran is trying to rally support from Russia, China and other countries to help counter a U.S. campaign that has included crippling economic sanctions and thousands of additional troops committed to the Middle East.

As Washington struggles to build robust international support for its pressure tactics against Tehran, Iranian officials are working to take advantage.

They highlight American dominance of the global financial system, which has irked Russia and China. They also warn against U.S. cyber and psychological warfare, themes that resonate in Moscow and Beijing.

The Iranian effort is on display this week at a summit in Ufa, Russia, where security officials from 119 nations have gathered. Among the participants is India, a key economic partner of Tehran, and China, which -- along with Russia, Germany, the U.K. and France -- is party to the 2015 multilateral nuclear deal with Iran that the U.S. exited last year.

In a speech, a top Iranian security official called on "the independent countries of the world" to break U.S. dominance of the financial system.

"The U.S. has destabilized the international security system with unilateralism and extraterritorial sanctions," Ali Shamkhani, secretary of Iran's Supreme National Security Council, said on Tuesday. "If a broad spectrum of countries decide to stand against the illegal blackmailing and bullying by the U.S., we can make the U.S. retreat."

The summit takes place amid growing tensions between the U.S. and Iran, following an attack on two tankers last week, which Washington blamed on Iran's Islamic Revolutionary Guard Corps.

This week, the U.S. said it would send an additional 1,000 troops to the Middle East in response to "hostile behavior" by Tehran, following a decision in May to deploy an extra 1,500 soldiers. Monday's commitment came the same day Iran said it would stockpile more enriched uranium in the next 10 days than allowed under the nuclear deal.

Iran has denied involvement in the tanker attack, and President Hassan Rouhani on Tuesday said Iran doesn't want a war with any nation, repeating a familiar line. Iran's military on Monday said if it wanted to block tankers in the Strait of Hormuz, it didn't need to lie about it.

China's top diplomat, Foreign Minister Wang Yi, on Tuesday said the U.S. risked opening a "Pandora's box" in its campaign against Iran and called on both countries to de-escalate, the Associated Press reported.

Russian Deputy Foreign Minister Sergei Ryabkov voiced support for Tehran, saying the international community needed to find ways to restore Iranian oil exports, Russian state media TASS reported.

Russian officials warned that the decision to increase the number of U.S. troops in the Middle East could destabilize the region.

"For quite a while, we have been witnessing the United States's continuous attempts to increase political, psychological, economic and military pressure on Iran," TASS reported Mr. Ryabkov as saying. "I think that such actions are rather provocative and cannot be considered as anything other than a deliberate policy to instigate a war."

Separately on Tuesday, Russian and Iranian energy ministers met in the Iranian city of Isfahan to continue discussions about an oil-for-goods program in which proceeds from sales of Iranian crude could pay for Russian equipment and agricultural products, Russian Energy Minister Alexander Novak told the Russian Rossiya 24 television channel.

Russia's interests aren't completely aligned with Iran's, though. The two countries are competing for influence in Syria as the war wraps up there. Next week, Nikolai Patrushev, secretary of the Russian Security Council, will meet U.S. national-security adviser John Bolton and Israeli security officials in Israel, an arch-foe of Iran.

In its own rallying efforts, the U.S. has called on the United Nations Security Council to impose sanctions on Tehran over its missile tests. Secretary of State Mike Pompeo has asked the council, of which Russia and China are members, to prevent Iran from circumventing an arms ban by authorizing inspections of ships in ports and stopping them in high waters. The council hasn't so far complied.

Traditional U.S. allies like the U.K. and Saudi Arabia have backed Mr. Pompeo and American military assertions that Iran orchestrated last week's tanker attacks and incidents in May that involved four other ships in the same area.

Iran has tried to cleave off European allies of the U.S., with limited success. Tehran framed its decision to exceed enriched-uranium limits as an ultimatum to European countries, pushing them to ensure Iran receives economic benefits from staying in the deal.

The European Union has expressed disapproval of the American campaign against Iran and its withdrawal from the nuclear deal, but officials like German Foreign Minister Heiko Maas have said any Iranian culpability in the tanker attacks would complicate efforts to help.

Georgi Kantchev and Thomas Grove in Moscow contributed to this article.

Write to Sune Engel Rasmussen at sune.rasmussen@wsj.com

(END) Dow Jones Newswires

June 18, 2019 14:54 ET (18:54 GMT)

Copyright (c) 2019 Dow Jones & Company, Inc.