Hollywood leading man George Clooney, who has said he was not suited for marriage, is engaged to British lawyer Amal Alamuddin, according to weekend media reports and a note from her law firm.

Alamuddin, 36, was spotted last week wearing a large ring at a Los Angeles restaurant where she and Clooney, 52, were apparently celebrating their engagement with friends, People magazine reported, citing anonymous sources.

"George and Amal are trying to keep things very low-key, but they also aren't really trying to hide this, it doesn't seem," said a source quoted by People. The New York Post also reported the couple's engagement.

On Monday, Alamuddin's London law firm seemed to confirmed the worst-kept secret in show business by sending congratulations to her and Clooney on their engagement.

"The barristers and staff of Doughty Street Chambers offer their best wishes and congratulations to Ms Amal Alamuddin, a member of Chambers, and Mr George Clooney on their engagement to be married," the firm said in a statement.

Clooney's representative, Stan Rosenfield, did not respond to an email from Reuters seeking confirmation. He told the Post on Friday that he did not comment on the actor's personal life.

Clooney and Alamuddin have been dating since October, according to media reports. The two-time Oscar winner has been married once, but since his 1993 divorce from Talia Balsam has remained one of Hollywood's most eligible bachelors.

'Bright Light'

Doughty Street Chambers said it had recruited Alamuddin in 2010 to complete her training as a barrister in England and she later became a full member, joining its international law team.

She was educated at St Hugh's College, Oxford University, and New York University School of Law and speaks Arabic and French fluently, according to the law firm's website.

Alamuddin has advised United Nations former secretary-general Kofi Annan on Syria, represented Ukraine's ex-prime minister Yulia Tymoshenko in challenging her detention before the European Court of Human Rights and has also represented WikiLeaks founder Julian Assange in extradition proceedings.

Alamuddin drew publicity last year when she was named as topping an online "hot list" of attractive female barristers in Britain.

Barrister Geoffrey Robertson, who took Alamuddin on at Doughty Street Chambers and worked with her on the Tymoshenko and Assange cases, described her as a "brilliant and passionate defender of human rights" who was respected by her colleagues.

The chief executive of her law firm, Robin Jackson, added his personal congratulations.

"She brings a bright light to everything she is involved in, and I am so delighted at her happy news," he said.