Pakistan's President Asif Ali Zardari arrived in Tehran Friday for a meeting with his two counterparts, Iran's Mahmoud Ahmedinejad and Afghanistan's Hamid Karzai.

Mr. Zardari also is expected to discuss with Mr. Ahmedinejad a range of bilateral issues, including the Iran-Pakistan gas pipeline project.

President Zardari's meetings in Iran come as relations between Islamabad and Washington are low following the covert U.S. raid deep into Pakistan to kill al-Qaida leader Osama bin Laden last month.

Relations between Afghanistan and the United States also are tense as President Karzai repeatedly has voiced his frustration over civilian casualties cause by coalition air strikes.

In addition to the three-way summit, the Afghan and Pakistani leaders are set to attend an anti-terrorism conference Saturday hosted by the Iranian government.

Sudan's President Omar al-Bashir, Iraqi President Jalal Talabani and Tajik President Emomali Rahmon also are expected to attend, as well as observers from other nations.