LONDON (Reuters) – State-backed Royal Bank of Scotland (RBS.L) aims to raise up to $4 billion from the share flotation of its U.S. bank Citizens Financial Group this month, it was announced on Monday, putting it on track to be the biggest U.S. bank share offering this year.

RBS, which is 81 percent owned by the UK government after being rescued in 2008, has come under pressure from UK regulators to improve its capital base and focus on its domestic business, and the bank had already made clear it planned to sell up to a quarter of Citizens this year through an initial public offer (IPO).

RBS said on Monday it would sell 140 million shares in Citizens at between $23 and $25 each in the New York IPO, and could sell a further 21 million shares in an over-allotment option granted to the underwriters of the offer.

Up to 29 percent of the bank will be sold, valuing Citizens at the top end of the price range at $14 billion.

RBS did not set a date for the listing, but it is slated for on or around Sept. 23, a person familiar with the matter said.

RBS said the sale would “significantly improve” its capital position and is “an important milestone” for both RBS and Citizens.

Analysts said once RBS sells at least half of Citizens, probably in the first half of next year, its core capital adequacy ratio should be boosted by 2-3 percentage points, although the initial IPO is unlikely to have much impact.

RBS has previously said it expects to fully sell out of Citizens by the end of 2016.

LONG HISTORY, SERIES OF DEALS

Citizens provides retail and commercial banking services to about 5 million customers in the United States and ranks as the country’s 13th biggest retail bank holding with about $130 billion in assets.

The 186-year-old bank, headquartered in Providence, Rhode Island, was bought by RBS in 1988 and expanded with 25 acquisitions, including the 2004 purchase of Charter One.

It has 18,000 staff and 1,200 branches in 11 states across the New England, Mid-Atlantic and Midwest regions at the end of June and made a net profit of $479 million in the six months to the end of June, on revenue of $2.6 billion.

Citizens is being valued at the upper end of the $9 billion to $15 billion range estimated by analysts with the IPO offer range pricing the business at near its net tangible book value of $13.1 billion at the end of June.

That represents a premium to RBS shares, which are trading at about 0.7 times book value. U.S. banks of a similar size, such as Fifth-Third (FITB.O) and BB&T Corp. (BBT.N), on average trade at near 1.2 times book value, according to Reuters data.

Citizens intends to list on the New York Stock Exchange under the trading symbol “CFG”.

Morgan Stanley (MS.N), Goldman Sachs (GS.N) and JPMorgan (JPM.N) are the lead advisors on the deal.

Shares in RBS dipped 1.3 percent on Monday, hurt by worries that it faces a further upheaval if Scottish residents votes in a referendum on Sept. 18 for independence, after a swing in support for the ‘Yes’ campaign in an opinion poll.