UNITED NATIONS – Secretary-General Annan is acting as mediator between Syrian President al-Assad and independent investigator Detlev Mehlis. Mr. Annan became involved after Mr. al-Assad sent a letter to Prime Minister Blair, asking for help in assuring that Mr. Mehlis’s interviews with Syrian suspects in the Hariri assassination would not be conducted in Lebanon.

Mr. Mehlis, who has been investigating the February assassination of the former Lebanese prime minister on behalf of the U.N. Security Council, has requested to interview at least six Syrians in the case, including Mr. al-Assad’s brother-in-law, Assef Shawkat. The inspector demanded that the interviews be conducted close to the crime scene in Beirut, where he also has full control over the proceedings. Lebanese authorities in the past have made arrests after Mr. Mehlis accused pro-Syrian Lebanese officials of complicity in the Hariri killing.

Syria refuses to send its officials to Lebanon. “Your wisdom, your understanding of the sensitivity of the Syrian-Lebanese issue, under these particular circumstances, and your well-known stances in relation to respecting the sovereignty and national laws of states are sufficient reasons for us to count on your support,” Mr. al-Assad wrote to Mr. Blair on Monday, according to a translation from Arabic seen by The New York Sun.

Mr. al-Assad offered alternative venues for the interviews, including the Arab League’s offices in Cairo or anywhere in Syria, specifically the U.N. offices in Damascus. Mr. Annan, who is on a tour of the Middle East, has spoken to Mr. al-Assad several times by phone, including on Tuesday, according to a U.N. spokeswoman, Marie Okabe. Mr. Annan has also praised Mr. Assad’s willingness to cooperate, as expressed in a speech last week. Describing the same speech, Secretary of State Rice said, “I don’t think this constitutes cooperation.”

A U.N. official traveling with Mr. Annan denied yesterday that the secretary-general is mediating, telling the Sun that Mr. Mehlis conducts the negotiations. But Western diplomats are worried that Mr. Annan has put himself in a position to influence the investigation, as he did last month in editing out the names of Mr. Shawkat and others from Mr. Mehlis’s report.

“Mehlis is the investigator,” American ambassador John Bolton told the Sun yesterday. “We want him to have unimpeded access to the evidence in Syria’s possession. And if he can’t get it, he can’t complete his investigation.” Mr. Mehlis’s mandate expires December 15, and he has indicated he would not extend his mission. American officials are concerned that time might run out before the investigation is complete.