In a leaflet distributed to correspondents in Gaza, Hamas complained that Mousa Abu-Marzuk had been prevented from entering the US, even though he had lived there for most of the past 14 years on a permanent-resident visa. Mr Abu-Marzuk's continued detention, Hamas added, "will increase the Arab and Muslim anger that is raging against the US's hostile policies." The leaflet warned the Americans against handing him over to "the Zionist occupation authorities."
Hamas is suspected of involvement in Monday's bus bombing in Tel Aviv in which six people died. But Israel is treading very cautiously before deciding whether to seek Mr Abu-Marzuk's extradition.
"We are interested in him, there is no doubt about that," the Justice Minister, David Libai, said yesterday.
"But we must prove that he committed a crime that is cause for extradition, and for this we must show evidence that stands up in court. The question is whether we have proof that connects him personally to terrorist acts."
According to Israeli intelligence, Mr Abu-Marzuk, 45, raised funds for Hamas in the US and sent couriers to deliver them to activists in Gaza and the West Bank. He fled the US two years ago after Islamic fundamentalists bombed the World Trade Centre in New York.
Until a month ago, when he was deported by Jordan at the request of Israel and the Palestine Liberation Organisation, the Israelis say he was masterminding Hamas resistance to the 1993 Oslo peace agreement from Amman.
Marwan Kanafani, spokesman for the PLO leader, Yasser Arafat, said yesterday, however, that Mr Abu-Marzuk would be welcome in Gaza if he had nowhere else to go. In that case, Israel is expected to exercise its continuing control of the Jordanian and Egyptian borders and try to keep him out.
A decision on requesting Mr Abu-Marzuk's extradition will be taken by the Prime Minister, Yitzhak Rabin, and the Foreign Minister, Shimon Peres, next week. Any application would have to clear judicial hurdles in both Israel, where a judge would be asked for an arrest warrant, and the US.
Mr Abu-Marzuk's arrest came three days before the planned resumption of Israeli-Palestinian peace negotiations, suspended by Mr Rabin after the Tel-Aviv bus blast. Neither side wants the arrest - or the bombing - to delay further an Israeli redeployment from West Bank Arab towns.
Israeli public opinion has reacted more stoically than it did after previous attacks. A poll published yesterday in Ma'ariv found an equal number (46 per cent) for and against continuing the peace talks. The poll was conducted one day after the bombing.
Commentators note that the right-wing opposition has failed this time to bring out masses of protesting Israelis. A columnist in the liberal daily Ha'aretz detected a growing maturity in Israeli public opinion.
"Logic says that a cessation of the peace process," wrote Ran Kislev, "will only escalate the attacks and might return the Palestine Liberation Organisation to the cycle of terror alongside the rejectionist organisations. If you want to limit terror, you must reduce the popular base on which terror feeds. The best way to achieve that is a peace agreement. This logic is taking hold more and more."