The Financial Times and Wall Street Journal reported on Monday that United Technologies was preparing an offer.

The FT said it values the company at �830m ($1.3bn).

Chubb said last week it had received an approach without identifying the bidder.

Neither Chubb nor United have reacted to the press reports.

The FT reported that United's chief financial officer Stephen Page said in February the company was looking for a big deal, a foreign takeover would be strongly considered and that it had between $1bn and $2bn to spend.

Shares surge

United's business interests include Pratt & Whitney jet engines, Sikorsky helicopters and Otis lifts.

Chubb business includes fire detection, CCTV, alarm monitoring and security personnel.

It has been the subject of takeover speculation since a talks with Swedish security giant Securitas broke down last year.

Analysts expect any offer for the company to be between �800m and �1bn.

Chubb's shares jumped by almost 30% when it announced a takeover was on the cards again, before settling back to close at 82p on Thursday.

Chubb listed on the stock market at 255p but hit a low of 49.75p in March over growth concerns.