At least two of the 26 suspects sought by Dubai police for the alleged killing of a top Hamas leader appear to have entered the U.S. shortly after his death, according to people familiar with the situation.

Records shared between international investigators show that one of the suspects entered the U.S. on Feb. 14, carrying a British passport, according to a person familiar with the situation. The other suspect, carrying an Irish passport, entered the U.S. on Jan. 21, according to this person. Senior Hamas leader Mahmoud al-Mabhouh's body was found in a Dubai hotel room on Jan. 20.

There aren't records of either man leaving the U.S., though investigators can't be sure the two are still in the country, according to this person. Since the two were traveling with what investigators believe to be fraudulently issued passports, they may have traveled back out of the U.S. with different, bogus travel documents.

The suspected U.S. travel broadens to American shores the international manhunt triggered by Dubai's investigation into the death of Mr. Mabhouh. Dubai police have already identified two U.S. financial companies they believe issued and distributed several credit cards used by 14 of the suspects in the alleged killing.

A U.S. State Department spokesman declined to comment.

A spokesman for Interpol, which is also investigating the murder, declined to comment.

Separately, Dubai police said Sunday that forensic results showed the drug succinylcholine in Mr. Mabhouh's bloodstream at the time of his death, suggesting he had been incapacitated by the muscle relaxant before being suffocated.

United Arab Emirates authorities have sought international arrest warrants for the 26 suspects, whom they caught on closed-circuit TV arriving at Dubai's airport and checking into their hotels. Some used disguises, and two of them shared an elevator ride with their alleged victim, according to footage released by police.

Dubai released photos, passports and travel details of the 26, all of whom had landed in Dubai with European or Australian passports. Many of the individuals identified by Dubai police surfaced within days. However, they looked nothing like the photos on the passports used in Dubai; the passport holders appeared instead to be victims of identity fraud. Britain, France, Ireland, Germany and Australia have all said they believe their passports were issued and used fraudulently in the case.

Dubai's police chief has said he is 99% certain that Israel's Mossad intelligence agency is behind the killing. But he hasn't provided any evidence. Other officials here appear more circumspect, and say Dubai and U.A.E. officials are concentrating on identifying and apprehending the suspects before blaming anyone.

Israeli officials have neither confirmed nor denied any involvement, a longstanding practice. Last week, Israel's foreign minister said there was no proof implicating Israel.

The investigation could prove an irritant to U.S.-Israeli ties if Mossad is implicated. European and Australian governments have called in their Israeli ambassadors demanding answers to how their passports were misused, though officials have stopped short of accusing Israel of involvement.

The U.A.E. government would seek the extradition of any suspects found in the U.S., said an Emirati official. If Israel was implicated, the Obama administration's relationship with that of Israeli Prime Minister Benjamin Netanyahu could come under further strain. Washington and Israel have publicly sparred in recent months on issues related to the resumption of peace talks between Israel and the Palestinians. The Obama administration says it is continuing to work with Israel on the possible resumption of peace talks, and U.S. officials say they are "hopeful" that negotiations can resume shortly.

According to the person familiar with the matter, one of the suspects, traveling with a British passport identifying him as Roy Allan Cannon, entered the U.S. on Feb. 14. Another suspect, traveling as Irishman Evan Dennings, entered the country on Jan. 21, a day after Mr. Mabhouh's body was discovered.

It wasn't clear from where either man was traveling. Dubai authorities have previously said the suspect traveling as Mr. Dennings left Dubai on Jan. 20 on his way to Zurich.

Last week, the Associated Press identified a British citizen named Roy Allan Cannon as having emigrated to Israel from Britain in 1979. His son told the AP his father was a victim of identity theft, and that "it's clear that illegal use was made of personal information." The Irish government said last week it believed Mr. Dennings was also the victim of identity fraud; he couldn't be reached for comment.