* Three Palestinians wounded by gunfire, hospitals say
* Israel says has detained 280 since teenagers disappeared
* Street battle in militant stronghold of Jenin
* At least six killed in Gaza militant tunnel explosion (Adds Netanyahu comment, rockets fired from Gaza into Israel)
By Maayan Lubell
HEBRON, West Bank, June 19 (Reuters) - Israeli forces traded gunfire with Palestinians on Thursday, the military said, in the fiercest street battles in the occupied West Bank since a search began for three Israeli teenagers missing for a week.
Hospital officials said three Palestinians suffered bullet wounds in the overnight clashes in Jenin, a militant stronghold and the scene of deadly fighting during a Palestinian uprising a decade ago. There were no reported Israeli casualties.
A military statement said about 300 Palestinians, including some who "hurled explosives and opened fire", confronted soldiers who entered Jenin looking for the three seminary students.
Israel says the Hamas Islamist group abducted them last Thursday as they were hitchhiking near a Jewish settlement.
"The soldiers responded with live fire, identifying hits," the statement said. It said 30 "terror suspects" were detained in the West Bank, bringing to 280 the number of Palestinians taken into custody over the past week.
Reuters photographers in Jenin heard heavy gunfire during the night but were kept away from the scene of the clashes by Israeli forces.
Israel has said its West Bank operation is twofold: to find Gil-Ad Shaer and U.S.-Israeli national Naftali Fraenkel, both aged 16, and Eyal Yifrah, 19, and to deal a substantial blow to Hamas, a group dedicated to its destruction.
A statement issued by the office of Palestinian President Mahmoud Abbas accused Israel of using the teenagers' disappearance as "a pretext to impose tough punishment against our people and besiege them" in violation of international humanitarian law.
Israeli raids have spread from house-to-house searches in Hebron, a flashpoint town in the area where the three went missing, to raids across the West Bank of institutions believed to provide funding and other support for Hamas.
"The policy of collective punishment conducted by the occupation government against our people and our land requires condemnation by the whole world," the Palestinian presidential statement said.
While military operations inside Hebron continued, the heavy troop presence around the city appeared to have been scaled back. Some roadblocks at entrances to the city were left unmanned, allowing vehicles to enter and leave freely. Paratrooper platoons that had camped by a road nearby were gone.
"We know more today than we did a few days ago, but we still have a way to go," Israeli Prime Minister Benjamin Netanyahu said at a West Bank military headquarters, near the site where the teens are believed to have been abducted.
As part of the crackdown, Israel said on Thursday it was banning the British-based charity Islamic Relief Worldwide (IRW) from operating in the occupied West Bank. It accuses the IRW of being a funding source for the Hamas Islamist movement.
At Bir Zeit University, near the Palestinian town of Ramallah, Israeli soldiers on Thursday seized Hamas posters and flags from a student group affiliated with Hamas.
Soldiers have searched about 900 locations so far, the military said. There has been no word from the missing teenagers nor any public claim of responsibility or ransom demands, including from Hamas.
Hamas, however, has not issued any denial of involvement and on Thursday appeared to praise the apparent abduction.
"Regardless of who was responsible for the operation ... the Palestinian people have the right to use all forms of resistance in order to liberate land and people," Hamas spokesman Sami Abu Zuhri said in a news conference in the Gaza Strip.
Hamas's armed wing in Gaza said at least six members of its group were killed in the collapse of a tunnel the group had dug close to the border with Israel to infiltrate the Jewish state.
Abbas roundly condemned the kidnappers on Wednesday and promised to hold to account those responsible. His words in turn were denounced by Hamas and other factions, who accused him of betraying the national cause.
Netanyahu called on Abbas and his more secular Fatah movement to turn their backs on Islamist Hamas, who have set up a unity government with the aim of healing a rift between the bitter Palestinian political rivals.
"I expect President Abbas to dissolve the union with this murderous terrorist organisation. I think that's important for our common future," the Israeli leader said.
On Tuesday, Hamas and 10 other Palestinian factions issued a joint communique warning Israel that they would not "stay handcuffed" in the face of its West Bank dragnet - a threat of armed resistance.
Later on Thursday, militants fired two rockets from the Gaza Strip into Israel, one of which was shot down by Israel's Iron Dome anti-missile interceptor system, the military said. Neither caused any damage.
Security experts expect the frustration of ordinary Palestinians at Israeli restrictions in the West Bank to mount as the Muslim fasting month of Ramadan is due to begin on June 28 or 29. (Additional reporting by Ali Sawafta in Ramallah and Nidal al-Mughrabi in Gaza; Writing by Jeffrey Heller and Ori Lewis in Jerusalem; Editing by Tom Heneghan and Jonathan Oatis)