Israeli soldiers rounded up at least seven of the Islamic militant group's political leaders in the West Bank in a pre-dawn arrest sweep Thursday, Hamas officials and relatives said.

The detentions come after the failure of recent efforts to win the release of an Israeli soldier Hamas is holding in Gaza.

The Israeli military, which routinely arrests suspected militants in the West Bank, said 20 Palestinians had been detained overnight. But it said it had no information on the arrests of the Hamas politicians.

Israel has detained dozens of Hamas politicians in the West Bank on various occasions since the capture of Sgt. Gilad Schalit, 22, in a cross-border raid in June 2006.

The detainees in this latest raid include Nasser Shaer, a former Palestinian deputy prime minister, and several Hamas lawmakers, Hamas officials and relatives said. Some of them were detained and released in past raids.

Outgoing Israeli Prime Minister Ehud Olmert had hoped to secure the release of Schalit before a new Israeli government is formed. He dispatched two senior envoys to Cairo over the weekend to try to clinch an Egyptian-brokered deal with Hamas, which rules Gaza and has no direct ties with Israel.

But the envoys returned to Israel without a deal. On Tuesday, Olmert declared that Israel would not free all of the hundreds of Palestinian prisoners the Islamic militants demanded in exchange for Schalit.

Some were involved in attacks that killed dozens of Israelis, and Olmert insisted that there were "red lines" that Israel "will not cross."

Incoming Prime Minister Benjamin Netanyahu, who is expected to partner with hawkish parties in Israel's new government, has not commented on the failed release efforts or how he plans to deal with Schalit's case.

The failure of the prisoner swap talks threatens to set off a long chain reaction of negative developments. Israel has vowed not to lift its crushing blockade of impoverished Gaza until Schalit is returned home. That could seriously impede reconstruction there after Israel's recent military offensive because building materials and equipment won't be able to enter the territory, home to 1.4 million Palestinians.

The continued blockade could also hamper efforts to cement a long-term truce between Israel and Hamas, which in turn would carry the threat of a sudden escalation in the low-level violence that has continued since the war ended on Jan. 18.