Assad flew into the capital's Mehrabad international airport and was driven straight to a meeting with President Mahmoud Ahmadinejad.

Iranian state-run television reported that in talks lasting more than an hour, "both sides emphasised the importance of Iranian-Syrian cooperation which is aimed at consolidating stability and security in the region."

Iran's ambassador to Syria Ahmad Moussavi said on Friday talks would include Iran's nuclear programme, which Western countries claim hides an ambition to develop atomic weapons but which Tehran says is purely for peaceful purposes.

"During the visit... the two sides will discuss... (Tehran's) nuclear issue," Moussavi was quoted as saying by the semi-official Fars news agency.

Local media reported that Assad would also meet Iran's Supreme Leader Ayatollah Ali Khamenei, who has the last word on major issues, before returning to Damascus on Sunday.

The Syrian's leader's visit follows a trip to Paris a month ago during which French President Nicolas Sarkozy urged Syria to "persuade Iran" to prove that it is not seeking nuclear weapons.

Assad's visit coincides with this weekend's US deadline for Iran to respond to an international offer of incentives for Tehran to freeze its nuclear drive amid warnings of new sanctions if it rejects the package.

White House spokeswoman Dana Perino warned: "Negative consequences await if they don't have a positive response to our very generous incentives package, and that would possibly come in the form of sanctions."

US Secretary of State Condoleezza Rice gave Iran two weeks to come up with a "serious" reply after an international meeting in Geneva on July 19 which saw Tehran broadly accused of stonewalling.

Perino said the United States would coordinate any action with its partners in the P5-plus-1, or the permanent UN Security Council members -- the United States, Russia, China, Britain and France -- plus Germany.

The P5-plus-1 has offered Iran benefits in civil nuclear energy, trade, finance, agriculture and high technology if it freezes uranium enrichment.

If Iran accepts the package, there would be pre-negotiations during which Tehran would add no more uranium-enriching centrifuges and, in return, face no further sanctions.

This trip is also Assad's first to Tehran since May, when Syria revived indirect talks with Iran's regional arch-foe Israel.

Iran does not recognise Israel, and Ahmadinejad has earned international notoriety for his verbal assaults on Israel, which he has described as a "stinking corpse" doomed to disappear.

The trip is Assad's third to Iran since Ahmadinejad was elected in 2005. He last visited in February 2007.

The Iran-Syria alliance, stretching back more than three decades, was strengthened in 2006 with the signing of a military cooperation agreement.

State television said that Iran is currently involved in a range of projects in Syria valued at around 1.3 billion dollars. It added that the two presidents also decided to boost bilateral economic, scientific and cultural links.

All rights reserved. � 2005 Agence France-Presse. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by Agence France-Presse. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of Agence France-Presse.