TEHRAN - President Mohammad Khatami's successful trip to Russia has caused frustration in U.S., which has always tried to isolate Iran from other countries, especially its neighbor Russia.

In a letter to President George W. Bush, U.S. lawmakers on Thursday expressed dissatisfaction over Tehran-Moscow talks, under the pretext of concern for possible arms sales from Russia to Iran. They urged the president to act "swiftly and appropriately."

"The strategic implications of Russia's arms transfers to Iran cannot be underestimated," said the letter signed by some 30 Democratic and Republican lawmakers of the compact agreed to by the two countries on March 12.

Russian National Security Advisor Sergei Ivanov on Wednesday dismissed U.S. concerns over his country's plans to sell arms to Iran, saying the deals would be legitimate and include only defensive weaponry.

Iranian president concluded his four-day visit to Moscow on Thursday. Upon arrival in Tehran he stressed that Tehran-Moscow cooperation does not contravene international conventions.

He dismissed foreign warnings that Iran-Russia cooperation might pose threat to other nations, saying, "Others should try to discipline themselves consistent with international conventions. We do not want to break those conventions."

He said that Iran and Russia had reached agreements on the controversial legal regime of the strategic Caspian Sea that had been the topic of debate among the five littoral states of Iran, Russia, Kazakhstan, Turkmenistan and Azerbaijan.

A Russian official said on Thursday Iran would sign up for a second Russian-built nuclear reactor once the delayed first one, which has already sparked U.S. worries, had been completed.

The Russian Deputy Foreign Minister Alexander Losyukov said here Thursday that Iran and Russia were now working on the phrasing of a joint statement at the end of President Khatami's landmark four-day visit to Russia.

No agreement has been signed for arms sale to Iran, he said, adding that the two countries' talks were only of political nature.

President Khatami in a meeting with Governor of St. Petersburg Vladimir Yakovlev Wednesday night said that Tehran-Moscow relations are based on national interests of the two nations in the benefit of bilateral progress and realization of regional and international peace.

President Khatami also conferred on Thursday with his Tatar counterpart Shaimiyev on issues of mutual interest. The meeting was held in Kazan the capital of Tatarstan.

Khatami described the destiny of all religions in Russia as interrelated and said they all try to glorify culture and religions.

The Tatar president, in response, expressed satisfaction with the visit of the Iranian president and expressed hope that the visit would open new horizons in two sides relations.