White House National Security Advisor Stephen Hadley said Iran represents the biggest challenge in the Middle East for the incoming administration of President-elect Barack Obama.

In remarks prepared for a speech in Washington Wednesday, Hadley warned against entering negotiations with Iran - a move Mr. Obama said he would consider. Hadley said by working with European partners, the new administration will have an opportunity to enforce tougher sanctions against Tehran.

Iran is under international sanctions over its disputed nuclear program. Tehran says it is only pursuing civilian nuclear applications, such as energy and medicine. The United States and others accuse Iran of seeking nuclear weapons.

Hadley said the Obama administration should also make it a priority to stabilize Pakistan in a broader effort to bring peace to Afghanistan and the rest of the region. He said the Taliban remains a serious threat in Afghanistan and its fighters have found safe haven across the border in Pakistan. Despite the recent violence in Gaza, Hadley said the biggest opportunity for the new administration may be peace between the Israelis and the Palestinians. He said Mr. Obama's team should build on the process that President George Bush established during talks with both sides in 2007. He said that means helping to build the democratic institutions of a future Palestinian state, and using confidential, bilateral talks between the sides to negotiate peace.

The national security advisor also warned of the challenges posed by Russia. He noted that the United States has worked together with Russia on certain issues. But he said the U.S.-Russia partnership is limited by Russia's failure to respect the rights of its people and its neighbors.

Hadley said if Russia continues to threaten its neighbors and manipulate their access to energy, it will compromise its aspirations for greater global influence.

Russia has cut gas supplies to Ukraine in an escalating price dispute. More than a dozen other European countries have reported gas cut-offs since January 1.

Hadley praised Mr. Bush's efforts to confront the global threat of terrorism. He said the biggest threat to the United States is the prospect of terrorists obtaining the world's most dangerous weapons.

Some information for this report was provided by AFP and AP.