Dublin-based pharmaceutical producer Shire, a specialist in drugs to treat rare diseases, has succumbed to an increased £31 billion ($53 billion) takeover offer from US drugmaker Abbvie, signaling the conclusion to a lengthy courtship largely motivated by tax benefits.

Shire said it would recommend the deal, the latest in a list of mergers proposed by US companies seeking to cut tax rates. It comes less than seven weeks after the collapse of Pfizer's $118 billion bid for AstraZeneca, also motivated in part by tax considerations.

AbbVie upped its order to £53.20 per share on July 13, following a request from Shire. Previously, it had rejected four bids.

Citing people familiar with the matter, the news agency Reuters reported earlier that Shire had asked AbbVie to sweeten its offer to nearly £53 per share in order for it to recommend the deal.

Shire said the new bid comprised £24.44 in cash and 0.8960 new AbbVie shares for each Shire share, giving Shire investors about 25 percent ownership of the combined entity.

AbbVie gets nearly 60% of its revenue from rheumatoid arthritis drug Humira, the world's top-selling medicine, which loses US patent protection in late 2016.

The approach for Shire has been far less controversial than the move for AstraZeneca. While headquartered in Dublin, Shire is managed from Boston and has most of its sales in the US,  resulting in a relatively small business footprint in the UK.

Shire Chief Executive Flemming Ornskov had said he was happy for the company to be sold at the right price.