The attack, which killed a Thai man working on a farm just inside Israel, embarrassed Hamas as UN officials in Gaza hosted the European Union's foreign affairs chief, a rare visit by such a senior Western official to the blockaded territory.
Analysts say the groups, which identify with Al-Qaeda but have no organizational links to it, do not pose an immediate threat to Hamas's rule over Gaza but are likely to remain a thorn in its side for some time to come.
The groups are accused of orchestrating a series of bomb attacks targeting Christian churches, Internet cafes and most recently Hamas security men and offices.
"They don't have a big following but they continually challenge the Hamas government and embarrass it by doing such attacks," said Are Hovdenak, author of a report on the subject for the International Peace Research Institute, Oslo (http://www.mil.no/multimedia/archive/00118/00092-118038a.pdf).
"The relationship between them (Hamas and Salafist groups) will continue to be tense," said Hovdenak.
Underlining the point, Thursday's rocket launch defied Hamas's efforts to rein in such attacks from Gaza, whose 1.5 million resident are suffering ever worsening living conditions due to a blockade enforced by Israel and Egypt.
The humanitarian situation in Gaza was exacerbated by an Israeli offensive launched in December 2008 with the stated aim of halting rocket fire from the Gaza Strip.
The three-week Israeli offensive killed 1,400 Palestinians and expert observers say that, despite its rhetoric, Hamas wants to avoid another round of heavy conflict for now.
Israeli Vice Prime Minister Silvan Shalom said Thursday's rocket attack had "crossed a red line.” "The Israeli response will be appropriate. It will be strong," he said. Previous attacks have drawn Israeli air strikes.
Hamas pioneered rocket strikes from Gaza and still backs armed struggle against Israel. It did not condemn the attack, saying Israel had brought it on through what Hamas described as provocations in Jerusalem. Hamas's refusal to renounce violence is among reasons it is shunned by Israel and the West.
However, the attack by a group called Ansar Al-Sunna during a visit by the EU's Catherine Ashton, who did not meet Hamas officials, is likely to encourage the group to further tighten its grip on radical dissidents.
Hamas security forces killed more than 20 people in Rafah last year when they stormed a mosque after a preacher challenged the group by declaring an Islamic emirate.
