By Josie Cox 

European investors were cautiously optimistic Tuesday, keeping an eye firmly on the lingering conflict in Ukraine but also pinning hopes on the European Central Bank announcing further stimulus measures at its policy meeting later in the week.

By mid-morning, the Stoxx Europe 600 had advanced 0.4%, broadly in line with Paris' CAC and London's FTSE. The latter, investors said, was likely also supported by U.K. construction PMI reaching its highest level for seven months in August. Germany's DAX gained 0.9%.

Several banks, including BNP Paribas and J.P. Morgan, have recently said they expect the ECB to take action at Thursday's meeting, possibly even including a broad-based asset purchase program knows as quantitative easing, to help bring inflation back up to target.

On Monday, data showed that activity in the euro zone's manufacturing sector slowed more sharply than first estimated in August, with Italy joining France in contraction, piling yet more pressure on the central bank to act.

"According to our economists, no rate cut and no major change in language to the ECB statement would be a key disappointment," BNP Paribas currency strategists wrote in a note. Gary Jenkins, a credit strategist at LNG Capital, meanwhile, described it as "a close call."

"My view is still that for [ECB] President Mario Draghi it remains a last resort, but he is in danger of being backed into a corner and left with little alternative but to enact QE at some stage," Mr. Jenkins added.

Mr. Draghi might also be fearful that even if QE is implemented, it might not work, leaving Europe still burdened with low growth and high unemployment, Mr. Jenkins said.

In currency markets, the euro was marginally weaker against the dollar, while Russia's ruble continued to slide steadily, following a heavy sell-off on Monday when it hit an all-time low against the dollar.

Ukrainian Defense Minister Valeriy Heletey said Monday that the army would stop trying to remove separatists from the east, moving instead to a defensive strategy against what he called a "full-scale invasion" of Russian regular troops.

His announcement of a change in tactics came as another round of talks between Kiev, Moscow and the separatists ended with no apparent results beyond agreeing to meet again Friday.

"A diplomatic solution in Ukraine still seems out of reach," Citigroup credit strategist Joseph Faith wrote in a note, while UBS economist Paul Donovan said that investors now appeared to be pricing in an escalation of European Union actions, in the form of more sanctions.

Elsewhere, the U.S. dollar jumped to a seven-month high against Japan's yen at 104.86 on Tuesday, on expectations that U.S. monetary stimulus is near an end, while in Japan hopes emerged that a cabinet reshuffle could lead to increased stakes in domestic stocks for the country's vast public pension fund.

The dollar has enjoyed support over the last few months, fueled by a raft of improving U.S. economic data, ranging from improving consumer confidence to better labor market conditions.

U.S. Federal Reserve officials signaled late last month that they were on track to end the QE program in October.

The U.K. pound meanwhile, came under pressure on a narrowing of opinion polls ahead of the vote on Scottish independence scheduled for Sept. 18.

A YouGov survey for the Sun newspaper and published Tuesday puts the lead for the 'no' campaign at just 6 percentage points when excluding undecided voters. That is down sharply from a previous 22-point lead recorded less than a month ago, and a 14-point lead seen mid-August, on the same basis.

The pound dipped 0.5% against the U.S. dollar to a five-month low of $1.6539. Some tip it for further falls. Daragh Maher, a currency strategist at HSBC, said it has the potential to slip to $1.6250 if the market starts adequately pricing in political risk.

"We've seen a degree of complacency in sterling about political risk in the U.K. The most recent polls, however, suggest that a 'no' vote is far from a guarantee," he said.

Back in European equities, Italy's Luxottica Group SpA, the world's largest eyewear maker, was one of the biggest losers of the day, on news that Andrea Guerra had stepped down as chief executive after almost 10 years.

In commodities markets Brent crude oil lost 0.1% to trade at $102.64 a barrel, while gold declined 0.4% to $1,282.50. In the U.S., the S&P 500 was seen opening 0.2% higher following Monday's Labor day holiday.

Futures, however, don't necessarily reflect moves after the opening bell.

Write to Josie Cox at josie.cox@wsj.com

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