Iran’s veneer of stoicism toward the Western sanctions that have disrupted its economy showed some new strains on Monday, as the deputy oil minister acknowledged a decline in domestic petroleum production because of dwindling foreign investment, and four-year-old talks between the Iranians and Poland’s biggest natural gas developer collapsed.

The Iranians also suffered an embarrassment after prematurely announcing that a Russian oil company had committed $1 billion to help revive a dormant oil field in Iran’s southwest. Hours later, the Russian company, Tatneft, denied on its Web site that a deal had been signed. And there were signals that Saudi Arabia, which Iran had confidently predicted last week would not increase oil production to compensate for any Iranian shortfall caused by the sanctions, was becoming increasingly irritated with Iran.

Together, the developments portrayed Iran, with the world’s fourth-largest oil reserves and second-largest natural gas reserves, as struggling more than it had admitted from the effects of the Western sanctions, despite its official denunciations of them as desperate measures doomed to fail or backfire.

The sanctions, imposed to pressure Iran into ending its suspect nuclear program, were strengthened last month, with the possibility of more onerous restrictions on Iran’s central bank and oil industry looming from the United States and the European Union. Under a measure that is likely to be signed into law by President Obama, foreign entities that do business with Iran’s central bank, the conduit for Iran’s oil revenue, could face severe penalties if they do business in the United States.