WASHINGTON (AFP) - US Secretary of State Hillary Clinton promised a sustained US diplomatic effort aimed at creating "an independent and viable" Palestinian state but renewed calls on Hamas to stop rocket fire. Clinton, who stood next to her special envoy George Mitchell after his return from his first trip to the Middle East, said he would return to the region before "the end of the month." "We are looking to work with all parties to try to help them make progress toward a negotiated agreement that would end the conflict between Israel and the Palestinians," Clinton told a press conference. The chief US diplomat vowed to work with all the parties to "create an independent and viable (Palestinian) state in both the West Bank and Gaza, and provide Israel with the peace and security that it has sought." She said: "We are going to work as hard as we can over what period of time is required." Clinton reiterated the goals of the preceding administration of George W Bush, who publicly called for the creation of a Palestinian state in the West Bank and Gaza Strip living next to a secure Israel. She vowed to work with the Palestinian Authority of Mahmud Abbas, who was also supported by the Bush administration and which operates only in the West Bank after it was ousted from Gaza in June 2007 by Hamas. Clinton renewed calls on Hamas to stop the rocket fire on Israel, which prompted Israel to launch a three-week invasion on December 27 that ended January 18 in a fragile truce. "Our conditions with respect to Hamas have not and will not change," Clinton told reporters as she stood next to returning Middle East envoy George Mitchell. "Hamas knows it must stop the rocket fire into Israel." Israeli warplanes on Tuesday bombed smuggling tunnels on Gaza's border with Egypt after the Jewish state warned of the "severest riposte" to rocket fire from the Hamas-run enclave, witnesses said. Clinton said Mitchell had returned from a week-long trip to Egypt, Israel, the West Bank, Jordan and Saudi Arabia, as the first part of "an ongoing high-level engagement on behalf of myself and the president" Barack Obama. "Senator Mitchell will be returning to the region before the end of the month," the chief US diplomat said. She also spoke of the political uncertainty in Israel. She added that she is "looking forward to the results of the Israeli elections so that we can begin working with a new Israeli government." Hawkish former prime minister Benjamin Netanyahu remains in a strong position to regain the premiership in the February 10 election, an opinion poll said Monday, with his Likud party expected to win 28 seats against a current 12. A rightwing coalition headed by Netanyahu would comprise 68 seats, giving it a clear parliamentary majority, according to the survey.