GAZA (Reuters) - Palestinian security forces detained dozens of supporters of Hamas in raids across the West Bank overnight, the Islamist group said on Monday, calling it the biggest round-up in years as internal Palestinian tensions rise.

A spokesman for the Palestinian Authority's security services confirmed that 30 people had been detained but denied the arrests were political. Hamas said the figure was closer to 80, but this could not be independently confirmed.

"Arrests are made in accordance with the law and not on grounds of political affiliation," said PA spokesman Adnan Al-Damiri. He described the offences as "criminal" and accused Hamas of incitement against the Palestinian Authority.

Hamas, which controls the Gaza Strip while also enjoying broad support in the Israeli-occupied West Bank, said those detained included party leaders, university students, writers and journalists affiliated with the movement.

The arrests follow the detention of tens of members of Fatah, the broadly secular mainstream faction headed by Palestinian President Mahmoud Abbas, in Gaza.

"We hold President Abbas personally responsible for the aggressive campaign against Hamas in the West Bank," said Fawzi Barhoum, a Hamas spokesman. "It is part of a dual campaign by the Zionist enemy (Israel) and the Palestinian Authority to uproot Hamas and the resistance."

While Hamas and Fatah agreed to form a unity government in April last year, a move that contributed to the breakdown of peace talks between Israel and Abbas, there has been little unity or cooperation between the rival factions.

Abbas is trying to ensure that Fatah remains the dominant political force in Palestinian politics, despite Hamas having narrowly won the last legislative elections in 2006.

As well as being squeezed by Fatah and Israel, Hamas has felt the wrath of Egypt's authorities, which are opposed to the Muslim Brotherhood, an ideological partner of Hamas.

The border crossing between Gaza and Egypt has largely been closed since 2013, with Egypt accusing Hamas of supplying weapons to Egyptian Islamist militants in Sinai, a charge Hamas denies. The border was briefly opened on Monday.

(Additional reporting by Ali Sawafta in Ramallah; Editing by Luke Baker)