HEBRON, West Bank, Dec 13 (Reuters) - Israeli soldiers punched two Reuters cameramen and forced them to strip in the street, before letting off a tear gas canister in front of them, leaving one of them needing hospital treatment.

Israel's military said on Thursday it took the allegations seriously, but offered no explanation for the assault that occurred on Wednesday evening in the heart of Hebron.

"The regional brigade commander was ordered to open an investigation," Israeli Defense Forces spokeswoman Avital Leibovich said in an email. No further information will be provided until the investigation is complete.

Yousri Al Jamal and Ma'amoun Wazwaz said a foot patrol stopped them as they were driving to a nearby checkpoint where a Palestinian teenager had just been shot dead by an Israeli border guard.

Their car was clearly marked 'TV' and they were both wearing blue flak jackets with 'Press' emblazoned on the front.

The soldiers forced them to leave the vehicle and punched them, striking them with the butts of their guns. They accused them of working for an Israeli NGO, B'Tselem, which documents human rights violations in the occupied West Bank, the Reuters cameramen said.

Locals say B'Tselem has given a number of Palestinians video cameras so they can film soldiers and settlers who live in this divided city. The NGO was not immediately available for comment.

The soldiers did not let the men produce their official ID papers and forced them to strip down to their underwear, making them kneel on the road with their hands behind their heads, the cameramen said.

Two other Palestinian journalists working for local news organisations, including a satellite television station affiliated to the Islamist group Hamas, were also stopped and forced to the ground.

One of the soldiers then dropped a tear gas canister between the men and the IDF patrol ran away. The four journalists scrambled clear and Jamal and Wazwaz got to their car, which had rapidly filled up with tear gas, they said.

They tried to drive away, but said they only got around 200 metres before they had to stop and exit the vehicle because of the choking gas. The soldiers then fired more tear gas in their direction.

Wazwaz was overcome by the fumes and was taken to hospital by ambulance. He was released later the same night.

The Israeli soldiers took two gas masks and a video camera from their car. The undamaged camera was later found abandoned further up the road.

"We deplore the mistreatment of our journalists and have registered our extreme dismay with the Israeli military authorities," said Stephen J. Adler, editor-in-chief of Reuters News.

Tensions have been running particularly high in Hebron in the past week following repeated clashes between stone-throwing youths and soldiers.

Muhammad al-Salameh, 17, was shot dead close to his house in the heart of Hebron on Wednesday evening after an altercation with border guards at a nearby checkpoint. Israeli police said he had brandished a gun, which later proved to be a toy gun.

Some 800 Jewish settlers live among 30,000 Palestinians in the parts of the old city that are under Israeli control.