• The al-Qassam Brigades military wing of the Islamist movement that rules the Gaza Strip has been banned in Britain since March 2001.
• "Hamas has significant terrorist capability, including access to extensive and sophisticated weaponry, as well as terrorist facilities," she tweeted.
Showing support for Hamas in Britain could be punished with 14 years in prison if the government succeeds in banning the group as a terrorist organisation, the Home Office said Friday.
Home Secretary Priti Patel will push for the change in parliament next week, seeking to bring Britain into line with the United States, which designated Hamas a terror group in 1995, and the European Union.
Patel argued an outright ban under the Terrorism Act 2000 was necessary because it was not possible to distinguish between Hamas' political and military wing.
The al-Qassam Brigades military wing of the Islamist movement that rules the Gaza Strip has been banned in Britain since March 2001.
"Hamas has significant terrorist capability, including access to extensive and sophisticated weaponry, as well as terrorist facilities," she tweeted.
"That is why today I have acted to proscribe Hamas in its entirety."
Patel, who is on a trip to Washington, called Hamas "fundamentally and rabidly anti-Semitic", adding that proscription was required to protect the Jewish community.
Israel's Prime Minister Naftali Bennett applauded the news, calling Hamas "a radical Islamic group that targets innocent Israelis and seeks Israel's destruction".
"I welcome the UK's intention to declare Hamas a terrorist organisation in its entirety -- because that's exactly what it is," he wrote on Twitter.
Foreign minister Yair Lapid said the move was a result of "joint efforts" between the British and Israeli governments.
If successful, flying Hamas' flag, arranging to meet its members or wearing clothing supporting the group will be outlawed.
Politically, it could force Britain's Labour party to take a position on Hamas, given strong pro-Palestinian support on the hard left of the main opposition party.
Former leader Jeremy Corbyn in 2016 said he regretted once calling members of Hamas and Hezbollah "friends" during a meeting at the British parliament.
Veteran socialist Corbyn, who said he was attempting "inclusive" language to encourage talks about the peace process, resigned after Labour's 2019 election drubbing.
Under his leadership, opponents alleged anti-Semitism went unchecked and even flourished, forcing Jewish members and lawmakers to leave the party in droves.
Earlier this month, a man appeared in court for wearing T-shirts supporting Hamas' military wing and Palestinian Islamic Jihad, which was banned in Britain in 2005.
On three occasions in June, Feras Al Jayoosi, 34, wore the garments in the Golders Green area of north London, which has a large Jewish population.