* Q2 op profit 4.78 bln SEK, beating all forecasts
* Costs and credit losses smaller than expected
* Says business activity picking up
* Warns financial regulations could hold back growth
* Shares up 2.5 pct, hit highest in five years (Adds Carlsson quote, details, share context, writes through)
By Mia Shanley and Oskar von Bahr
STOCKHOLM, July 15 (Reuters) - Swedish bank SEB has reported an unexpected surge in quarterly profit, saying a growing number of companies were setting aside doubts over the economy to seek funds for long-delayed investments.
Its shares jumped more than 2 percent to a five-year high.
SEB, with clients including 2,800 large companies and institutions, said on Monday it had won 52 major new corporate clients in the first half year in the Nordics and Germany.
"It's easing up a little bit, the concerns that our clients have had, and they are daring to do business," Magnus Carlsson, SEB's head of merchant banking, told a news conference. "My gut feeling is that is going to continue quite strongly."
Such comments represent a change in tone from corporate-focused SEB, which has suffered from sluggish lending to business since the global financial crisis.
"What SEB noted was that they see higher customer activity and I think that's very good news," said Kimmo Rama, an analyst at brokerage Evli. "The Swedish economy has now rebounded."
But SEB Chief Executive Annika Falkengren also warned that the recovery could be more muted if regulators further tighten rules on how much capital banks must hold, which could restrict their ability to lend.
In the meantime SEB has benefited from surprisingly strong Swedish growth at the start of 2013, after the economy slowed last year when the euro zone debt crisis hit companies such as truck maker Volvo and appliance maker Electrolux .
Mergers, acquisitions and capital market activities picked up in the first quarter and SEB noted good demand for financing for infrastructure projects and a greater appetite for structured loans in shipping and real estate.
Bond activity was also strong, with SEB serving as joint bookrunner for issues from telecoms firm Telenor, some of which funded the purchase of Bulgaria's second-biggest mobile operator, and from Nasdaq OMX Group, which acquired the trading platform eSpeed in the quarter.
A feather in its cap was the Swedish state's $3.0 billion stake sale in Nordea Bank AB, for which it served as joint bookrunner.
SEB posted a near 30 percent rise in operating profit to 4.78 billion Swedish crowns ($703 million) in the second quarter through June, beating every forecast in a Reuters poll.
SEB, which has had weaker returns than peers, said its return on equity reached 14.0 percent compared with 11.0 percent in the previous quarter. The bank also beat expectations on all quarterly income lines, while net credit losses were lower than expected.
Its shares were up 2.5 percent by 1041 GMT, outperforming Stockholm's blue-chip index which was up 0.4 percent. Rival Swedish banks Nordea and Swedbank, which also report this week, were also trading higher.
Falkengren said she was concerned that banking authorities might push through tighter benchmarks for minimum bank capital.
The Basel Committee of global regulators has set out a "leverage ratio" goal for bank capital to represent no less than 3 percent of assets, but there is pressure for the target to be raised further to reduce the risk of more banks being bailed out by governments.
Swedish banks already meet the proposed requirement, but on average they are below the international average of 3.8 percent, according to the central bank.
Falkengren said the risk of the cumulative regulatory effects hampering economic growth could not be ruled out.
"We work so hard in a Basel III world, so of course it's very challenging if they come back and say we are going to do it differently," she told Reuters.
Nordic banks are generally more sceptical about the leverage ratio, saying it does not take into account their larger holdings of low-risk mortgage loan portfolios compared with other European counterparts. (Editing by Tom Pfeiffer and David Holmes)