Members of the Salah al-Din Brigades fired a Qassam rocket at the western Negev Thursday morning. The rocket landed in an open area, and no damage or injuries were reported.
Palestinian armed factions renewed their commitment to a Gaza Strip truce on Thursday but said rocket barrages from the territory could resume if Israel did not halt military operations in the West Bank.
The message was delivered to Israel by an Egyptian mediator who has been trying to prevent a major confrontation after Hamas's armed wing fired rockets and declared the Gaza truce dead on Tuesday, Palestinians familiar with the talks said.
The Popular Resistance Committees (PRC) denied any agreement between Palestinian factions to uphold the ceasefire.
PRC spokesman Abu Abir told Ynet that the report was false, and that there would be no ceasefire as long as there was Israeli aggression in the West Bank and the Gaza Strip.
Israeli Prime Minister Ehud Olmert and Palestinian President Mahmoud Abbas agreed on the truce in November, but rocket fire has continued sporadically. Hamas's Izz el-Deen al-Qassam Brigades called Tuesday's barrage a response to the killing of eight Palestinians in Israeli military operations, most of them in the West Bank.
Israel has in the past signaled its interest in extending the Gaza truce to the West Bank, but only if militant threats cease first. Israeli officials were not immediately available for comment on the apparent ultimatum delivered by Hammad.
Olmert warned on Wednesday that he could authorize a major military action in Gaza, but for the time being he has limited Israel's response to the rockets from Gaza, which rarely cause serious casualties.
"Israel will not hesitate to take harsh measures against those who try to harm its sovereignty by firing rockets ... and other means," Olmert's office said after he convened security chiefs to discuss Hamas's barrage, in which no one was hurt.
Abbas, whose secular Fatah faction formed a ruling coalition with Hamas last month, called Tuesday's rockets "an exceptional event that will not last" and urged restraint by Israel.
Shmulik Haddad and Ali Waked contributed to this article