* Israel blames Islamist Hamas for abduction
* Raids and arrests have triggered street clashes
* Hamas has neither confirmed nor denied involvement (Adds 15 Palestinian institutions raided, Hamas comment)
By Ali Sawafta
RAMALLAH, West Bank, June 21 (Reuters) - Israel sent more troops to the occupied West Bank on Saturday to search for three missing teenagers it says were abducted by Palestinian Islamist group Hamas.
The military said it arrested 10 Palestinians on Saturday and that some 1,350 sites in the West Bank had been searched so far and more than 330 Palestinians detained.
The raids have triggered street clashes in the West Bank in which two Palestinians have been killed.
Hamas, which refuses to recognise Israel's existence, has neither claimed nor denied responsibility for the disappearance of the youths, who went missing near an Israeli settlement on June 13.
Hundreds of troops were deployed around the city of Hebron on Saturday, a day after the army declared the area a closed military zone, and appeared to be carrying out searches, a Reuters witness said.
Overnight in Ramallah, troops raided the offices of a media broadcast and production company, witnesses said.
An Israeli military spokeswoman said the soldiers found "electronic devices and magnetic media used for terrorism" that she said belonged to Hamas, without going into further detail.
Israel has also hit welfare organisations it accuses of aiding Hamas. Soldiers raided 30 such institutions on Thursday and 15 more on Saturday, a military spokesman said.
Campaign group The Palestinian Prisoners Club said the army had arrested 37 people on Saturday.
Palestinian President Mahmoud Abbas has condemned the kidnapping of Gil-Ad Shaer and U.S.-Israeli national Naftali Fraenkel, both aged 16, and Eyal Yifrah, 19.
But the Western-backed leader has also criticised the extent of Israel's recent raids, saying they amount to collective punishment.
The crisis has put pressure on a unity pact between Abbas's Fatah party and Hamas. Palestinian Foreign Minister Riad al-Malki told Reuters on Friday the deal would be threatened if Hamas was responsible for abducting the three youths.
Hamas spokesman Fawzi Barhoum said on his Facebook page al-Malki's comments were "irresponsible".
Hamas controls the Gaza Strip, an area that, along with East Jerusalem and the West Bank, Palestinians want for a future state. The group rejects peace talks with Israel, which Abbas has held in the past.
Hamas spokesman Sami Abu Zuhri said in Gaza on Thursday that "regardless of who was responsible (for the teenagers' disappearance) ... we stress on the right of our people to react to the agonies of our prisoners in the occupation jails". (Additional reporting by Nidal al-Mughrabi and Baz Ratner in Hebron; Writing by Maayan Lubell; Editing by Andrew Roche)