The Russian secret service said it intercepted details of a plot by Iranians to kidnap or kill the Russian president by suicide bomb while he is in Tehran

Mr. Putin is traveling to Tehran to attend a summit of states bordering the Caspian to settle a long-standing dispute over how much of the riches of the inland sea each nation is entitled to.

Azerbaijan and Kazakhstan, want the undersea resources, thought to contain vast reserves of oil and gas, divided according to how many miles of Caspian coast each nation has. Iran wants the resources divided equally among the five nations, which include Turkmenistan. The Russian plan would sharply reduce Iran's share of the spoils to 13% from 20%.

Around the edges of the Caspian conference, Messrs. Putin and Ahmadinejad are expected to discuss ways to defuse the standoff between America and its Western allies and Iran over the enrichment of uranium and the Islamic nation's nuclear ambitions.