(Updates for European mid-session trading)

* Strait of Hormuz at standstill remains a worry for

investors

* Iran rejected last round of talks before ceasefire

extension

* It remains to be seen if Iran or Israel agrees to

extend ceasefire

* Gunfire on ships sparks concerns

By Lawrence White

LONDON, April 22 (Reuters) - U.S. stock futures rose,

while the dollar wavered and oil prices edged up on Wednesday,

after reports of gunfire attacks on container ships in the

Strait of Hormuz immediately tested President Donald Trump's

unilateral declaration of an Iran ceasefire extension.

Brent crude futures were up 73 cents, or 0.7%, at

$99.15 a barrel while West Texas Intermediate futures

were up 59 cents, or 0.7%, to $90.2, after at least three

container ships were hit by gunfire in the Strait which has

become a flashpoint in the ongoing conflict.

It was not clear whether Trump's announcement of an

indefinite pause in hostilities would be backed by U.S. ally

Israel or Iran, which had already rejected a second round of

negotiations.

S&P futures rose 0.5% while Nasdaq futures

gained 0.7%. Europe's benchmark STOXX index was flat,

while MSCI's broadest index of Asia-Pacific shares outside Japan

dropped 0.5% after hitting a seven-week high on

Tuesday.

Bond yields barely moved, as investors held off making big

bets while waiting for more concrete signs as to whether the

simmering tensions in the Middle East were headed for a

near-term resolution or likely to keep building.

HORMUZ REMAINS KEY

Although the war caused a sharp selloff in March, equity

markets across the globe have rebounded this month to pre-war

levels as the prospect of a peace deal and the ceasefire spurred

a risk-on rally.

That has also left the U.S. dollar, which benefited from

safe haven demand in March, on the back foot, giving up most of

its war-induced gains.

"It appears markets were right to assume peak war

uncertainty is behind us," said Matt Simpson, a senior market

analyst at StoneX. "Risk seems likely to remain buoyant and dips

viewed favourably by equity bulls. The closure of the Strait of

Hormuz is already priced in."

The dollar index, which measures the U.S. currency

against six others, was last at 98.33. Although it is hovering

near its highest in a week, it is down 1.5% in April after

rising about 2.3% in March.

Trump said he would continue the U.S. Navy's blockade of

Iran's ports and shores.

While oil prices have come down from their March peaks they

are still well above pre-war levels, worrying investors that

elevated energy prices could quicken inflation and keep global

interest rates higher for longer.

WARSH SENATE APPEARANCE

Investors parsed comments from Federal Reserve chief nominee

Kevin Warsh as he tried to assure U.S. senators considering his

confirmation to lead the central bank that he ​would act

independently of the White House.

Warsh said he had made no promises to Trump about cutting

rates and called for a new approach to controlling inflation and

a communications overhaul that could discourage his colleagues

from saying too much about the direction of monetary policy.

Separately, data on Tuesday showed U.S. retail sales rose more

than expected in March as the war with Iran boosted gasoline

prices and led to a record surge in receipts at service

stations, while tax refunds underpinned spending elsewhere.